gregor mendel and his experiment on garden peas

Mendel's Experiments: The Study Of Pea Plants & Inheritance

** Gregor Mendel ** was a 19th-century pioneer of genetics who today is remembered almost entirely for two things: being a monk and relentlessly studying different traits of pea plants. Born in 1822 in Austria, Mendel was raised on a farm and attended the University of Vienna in Austria's capital city.

There, he studied science and math, a pairing that would prove invaluable to his future endeavors, which he conducted over an eight-year period entirely at the monastery where he lived.

In addition to formally studying the natural sciences in college, Mendel worked as a gardener in his youth and published research papers on the subject of crop damage by insects before taking up his now-famous work with Pisum sativum, the common pea plant. He maintained the monastery greenhouses and was familiar with the artificial fertilization techniques required to create limitless numbers of hybrid offspring.

An interesting historical footnote: While Mendel's experiments and those of the visionary biologist ** Charles Darwin ** both overlapped to a great extent, the latter never learned of Mendel's experiments.

Darwin formulated his ideas about inheritance without knowledge of Mendel's thoroughly detailed propositions about the mechanisms involved. Those propositions continue to inform the field of biological inheritance in the 21st century.

Understanding of Inheritance in the Mid-1800s

From the standpoint of basic qualifications, Mendel was perfectly positioned to make a major breakthrough in the then-all-but-nonexistent field of genetics, and he was blessed with both the environment and the patience to get done what he needed to do. Mendel would end up growing and studying nearly 29,000 pea plants between 1856 and 1863.

When Mendel first began his work with pea plants, the scientific concept of heredity was rooted in the concept of blended inheritance, which held that parental traits were somehow mixed into offspring in the manner of different-colored paints, producing a result that was not quite the mother and not quite the father every time, but that clearly resembled both.

Mendel was intuitively aware from his informal observation of plants that if there was any merit to this idea, it certainly didn't apply to the botanical world.

Mendel was not interested in the appearance of his pea plants per se. He examined them in order to understand which characteristics could be passed on to future generations and exactly how this occurred at a functional level, even if he didn't have the literal tools to see what was occurring at the molecular level.

Pea Plant Characteristics Studied

Mendel focused on the different traits, or characters, that he noticed pea plants exhibiting in a binary manner. That is, an individual plant could show either version A of a given trait or version B of that trait, but nothing in between. For example, some plants had "inflated" pea pods, whereas others looked "pinched," with no ambiguity as to which category a given plant's pods belonged in.

The seven traits Mendel identified as being useful to his aims and their different manifestations were:

• Flower color:  Purple or white. • Flower position:  Axial (along the side of the stem) or terminal (at the end of the stem). • Stem length:  Long or short. • Pod shape:  Inflated or pinched. • Pod color:  Green or yellow. • Seed shape:  Round or wrinkled. • Seed color:  Green or yellow.

Pea Plant Pollination

Pea plants can self-pollinate with no help from people. As useful as this is to plants, it introduced a complication into Mendel's work. He needed to prevent this from happening and allow only cross-pollination (pollination between different plants), since self-pollination in a plant that does not vary for a given trait does not provide helpful information.

In other words, he needed to control what characteristics could show up in the plants he bred, even if he didn't know in advance precisely which ones would manifest themselves and in what proportions.

Mendel's First Experiment

When Mendel began to formulate specific ideas about what he hoped to test and identify, he asked himself a number of basic questions. For example, what would happen when plants that were true-breeding for different versions of the same trait were cross-pollinated?

"True-breeding" means capable of producing one and only one type of offspring, such as when all daughter plants are round-seeded or axial-flowered. A true line shows no variation for the trait in question throughout a theoretically infinite number of generations, and also when any two selected plants in the scheme are bred with each other.

• To be certain his plant lines were true, Mendel spent two years creating them.

If the idea of blended inheritance were valid, blending a line of, say, tall-stemmed plants with a line of short-stemmed plants should result in some tall plants, some short plants and plants along the height spectrum in between, rather like humans. Mendel learned, however, that this did not happen at all. This was both confounding and exciting.

Mendel's Generational Assessment: P, F1, F2

Once Mendel had two sets of plants that differed only at a single trait, he performed a multigenerational assessment in an effort to try to follow the transmission of traits through multiple generations. First, some terminology:

• The parent generation was the P generation , and it included a P1 plant whose members all displayed one version of a trait and a P2 plant whose members all displayed the other version. • The hybrid offspring of the P generation was the F1 (filial) generation . • The offspring of the F1 generation was the  F2 generation  (the "grandchildren" of the P generation).

This is called a _ monohybrid cross _: "mono" because only one trait varied, and "hybrid" because offspring represented a mixture, or hybridization, of plants, as one parent has one version of the trait while one had the other version.

For the present example, this trait will be seed shape (round vs. wrinkled). One could also use flower color (white vs. purpl) or seed color (green or yellow).

Mendel's Results (First Experiment)

Mendel assessed genetic crosses from the three generations to assess the heritability of characteristics across generations. When he looked at each generation, he discovered that for all seven of his chosen traits, a predictable pattern emerged.

For example, when he bred true-breeding round-seeded plants (P1) with true-breeding wrinkled-seeded plants (P2):

• All of the plants in the F1 generation had round seeds . This seemed to suggest that the wrinkled trait had been obliterated by the round trait.  • However, he also found that, while about three-fourths of the plants in the F2 generation has round seeds, about one-fourth of these plants had wrinkled seeds . Clearly, the wrinkled trait had somehow "hidden" in the F1 generation and re-emerged in the F2 generation.

This led to the concept of dominant traits (here, round seeds) and recessive traits (in this case, wrinkled seeds).

This implied that the plants' _ phenotype (what the plants actually looked like) was not a strict reflection of their genotype _ (the information that was actually somehow coded into the plants and passed along to subsequent generations).

Mendel then produced some formal ideas to explain this phenomenon, both the mechanism of heritability and the mathematical ratio of a dominant trait to a recessive trait in any circumstance where the composition of allele pairs is known.

Mendel's Theory of Heredity

Mendel crafted a theory of heredity that consisted of four hypotheses:

1. Genes  (a gene being the chemical code for a given trait) can come in different types. 2. For each characteristic, an organism inherits one  allele  (version of a gene) from each parent. 3. When two different alleles are inherited, one may be expressed while the other is not. 4. When gametes (sex cells, which in humans are sperm cells and egg cells) are formed, the two alleles of each gene are separated.

The last of these represents the ** law of segregation **, stipulating that the alleles for each trait separate randomly into the gametes.

Today, scientists recognize that the P plants that Mendel had "bred true" were homozygous for the trait he was studying: They had two copies of the same allele at the gene in question.

Since round was clearly dominant over wrinkled, this can be represented by RR and rr, as capital letters signify dominance and lowercase letters indicate recessive traits. When both alleles are present, the trait of the dominant allele was manifested in its phenotype.

The Monohybrid Cross Results Explained

Based on the foregoing, a plant with a genotype RR at the seed-shape gene can only have round seeds, and the same is true of the Rr genotype, as the "r" allele is masked. Only plants with an rr genotype can have wrinkled seeds.

And sure enough, the four possible combinations of genotypes (RR, rR, Rr and rr) yield a 3:1 phenotypic ratio, with about three plants with round seeds for every one plant with wrinkled seeds.

Because all of the P plants were homozygous, RR for the round-seed plants and rr for the wrinkled-seed plants, all of the F1 plants could only have the genotype Rr. This meant that while all of them had round seeds, they were all carriers of the recessive allele, which could therefore appear in subsequent generations thanks to the law of segregation.

This is precisely what happened. Given F1 plants that all had an Rr genotype, their offspring (the F2 plants) could have any of the four genotypes listed above. The ratios were not exactly 3:1 owing to the randomness of the gamete pairings in fertilization, but the more offspring that were produced, the closer the ratio came to being exactly 3:1.

Mendel's Second Experiment

Next, Mendel created _ dihybrid crosses _, wherein he looked at two traits at once rather than just one. The parents were still true-breeding for both traits, for example, round seeds with green pods and wrinkled seeds with yellow pods, with green dominant over yellow. The corresponding genotypes were therefore RRGG and rrgg.

As before, the F1 plants all looked like the parent with both dominant traits. The ratios of the four possible phenotypes in the F2 generation (round-green, round-yellow, wrinkled-green, wrinkled-yellow) turned out to be 9:3:3:1

This bore out Mendel's suspicion that different traits were inherited independently of one another, leading him to posit the ** law of independent assortment **. This principle explains why you might have the same eye color as one of your siblings, but a different hair color; each trait is fed into the system in a manner that is blind to all of the others.

Linked Genes on Chromosomes

Today, we know the real picture is a little more complicated, because in fact, genes that happen to be physically close to each other on chromosomes can be inherited together thanks to chromosome exchange during gamete formation.

In the real world, if you looked at limited geographical areas of the U.S., you would expect to find more New York Yankees and Boston Red Sox fans in close proximity than either Yankees-Los Angeles Dodgers fans or Red Sox-Dodgers fans in the same area, because Boston and New York are close together and both are close to 3,000 miles from Los Angeles.

Mendelian Inheritance

As it happens, not all traits obey this pattern of inheritance. But those that do are called Mendelian traits . Returning to the dihybrid cross mentioned above, there are sixteen possible genotypes:

RRGG, RRgG, RRGg, RRgg, RrGG, RrgG, RrGg, Rrgg, rRGG, rRgG, rRGg, rRgg, rrGG, rrGg, rrgG, rrgg

When you work out the phenotypes, you see that the probability ratio of

round green, round yellow, wrinkled green, wrinkled yellow

turns out to be 9:3:3:1. Mendel's painstaking counting of his different plant types revealed that the ratios were close enough to this prediction for him to conclude that his hypotheses were correct.

• Note: A genotype of rR is functionally equivalent to Rr. The only difference is which parent contributes which allele to the mix.

• Scitable by Nature Education: Gregor Mendel and the Principles of Inheritance
• Biology LibreTexts: Mendel's Pea Plants
• OpenText BC: Concepts of Biology: Laws of Inheritance
• Forbes Magazine: How Mendel Channeled Darwin

Cite This Article

Beck, Kevin. "Mendel's Experiments: The Study Of Pea Plants & Inheritance" sciencing.com , https://www.sciencing.com/mendels-experiments-the-study-of-pea-plants-inheritance-13718433/. 8 May 2019.

Beck, Kevin. (2019, May 8). Mendel's Experiments: The Study Of Pea Plants & Inheritance. sciencing.com . Retrieved from https://www.sciencing.com/mendels-experiments-the-study-of-pea-plants-inheritance-13718433/

Beck, Kevin. Mendel's Experiments: The Study Of Pea Plants & Inheritance last modified August 30, 2022. https://www.sciencing.com/mendels-experiments-the-study-of-pea-plants-inheritance-13718433/

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21 Mendel’s Experiments

By the end of this section, you will be able to:

• Explain the scientific reasons for the success of Mendel’s experimental work
• Describe the expected outcomes of monohybrid crosses involving dominant and recessive alleles

Johann Gregor Mendel (1822–1884) (Figure 1) was a lifelong learner, teacher, scientist, and man of faith. As a young adult, he joined the Augustinian Abbey of St. Thomas in Brno in what is now the Czech Republic. Supported by the monastery, he taught physics, botany, and natural science courses at the secondary and university levels. In 1856, he began a decade-long research pursuit involving inheritance patterns in honeybees and plants, ultimately settling on pea plants as his primary model system (a system with convenient characteristics that is used to study a specific biological phenomenon to gain understanding to be applied to other systems). In 1865, Mendel presented the results of his experiments with nearly 30,000 pea plants to the local natural history society. He demonstrated that traits are transmitted faithfully from parents to offspring in specific patterns. In 1866, he published his work, Experiments in Plant Hybridization, 1 in the proceedings of the Natural History Society of Brünn.

Mendel’s work went virtually unnoticed by the scientific community, which incorrectly believed that the process of inheritance involved a blending of parental traits that produced an intermediate physical appearance in offspring. This hypothetical process appeared to be correct because of what we know now as continuous variation. Continuous variation is the range of small differences we see among individuals in a characteristic like human height. It does appear that offspring are a “blend” of their parents’ traits when we look at characteristics that exhibit continuous variation. Mendel worked instead with traits that show discontinuous variation . Discontinuous variation is the variation seen among individuals when each individual shows one of two—or a very few—easily distinguishable traits, such as violet or white flowers. Mendel’s choice of these kinds of traits allowed him to see experimentally that the traits were not blended in the offspring as would have been expected at the time, but that they were inherited as distinct traits. In 1868, Mendel became abbot of the monastery and exchanged his scientific pursuits for his pastoral duties. He was not recognized for his extraordinary scientific contributions during his lifetime; in fact, it was not until 1900 that his work was rediscovered, reproduced, and revitalized by scientists on the brink of discovering the chromosomal basis of heredity.

Mendel’s Crosses

Mendel’s seminal work was accomplished using the garden pea, Pisum sativum , to study inheritance. This species naturally self-fertilizes, meaning that pollen encounters ova within the same flower. The flower petals remain sealed tightly until pollination is completed to prevent the pollination of other plants. The result is highly inbred, or “true-breeding,” pea plants. These are plants that always produce offspring that look like the parent. By experimenting with true-breeding pea plants, Mendel avoided the appearance of unexpected traits in offspring that might occur if the plants were not true-breeding. The garden pea also grows to maturity within one season, meaning that several generations could be evaluated over a relatively short time. Finally, large quantities of garden peas could be cultivated simultaneously, allowing Mendel to conclude that his results did not come about simply by chance.

Mendel performed hybridizations , which involve mating two true-breeding individuals that have different traits. In the pea, which is naturally self-pollinating, this is done by manually transferring pollen from the anther of a mature pea plant of one variety to the stigma of a separate mature pea plant of the second variety.

Plants used in first-generation crosses were called P , or parental generation, plants (Figure 2). Mendel collected the seeds produced by the P plants that resulted from each cross and grew them the following season. These offspring were called the F 1 , or the first filial (filial = daughter or son), generation. Once Mendel examined the characteristics in the F 1 generation of plants, he allowed them to self-fertilize naturally. He then collected and grew the seeds from the F 1 plants to produce the F 2 , or second filial, generation. Mendel’s experiments extended beyond the F 2 generation to the F 3 generation, F 4 generation, and so on, but it was the ratio of characteristics in the P, F 1 , and F 2 generations that were the most intriguing and became the basis of Mendel’s postulates.

Garden Pea Characteristics Revealed the Basics of Heredity

In his 1865 publication, Mendel reported the results of his crosses involving seven different characteristics, each with two contrasting traits. A trait is defined as a variation in the physical appearance of a heritable characteristic. The characteristics included plant height, seed texture, seed color, flower color, pea-pod size, pea-pod color, and flower position. For the characteristic of flower color, for example, the two contrasting traits were white versus violet. To fully examine each characteristic, Mendel generated large numbers of F 1 and F 2 plants and reported results from thousands of F 2 plants.

What results did Mendel find in his crosses for flower color? First, Mendel confirmed that he was using plants that bred true for white or violet flower color. Irrespective of the number of generations that Mendel examined, all self-crossed offspring of parents with white flowers had white flowers, and all self-crossed offspring of parents with violet flowers had violet flowers. In addition, Mendel confirmed that, other than flower color, the pea plants were physically identical. This was an important check to make sure that the two varieties of pea plants only differed with respect to one trait, flower color.

Once these validations were complete, Mendel applied the pollen from a plant with violet flowers to the stigma of a plant with white flowers. After gathering and sowing the seeds that resulted from this cross, Mendel found that 100 percent of the F 1 hybrid generation had violet flowers. Conventional wisdom at that time would have predicted the hybrid flowers to be pale violet or for hybrid plants to have equal numbers of white and violet flowers. In other words, the contrasting parental traits were expected to blend in the offspring. Instead, Mendel’s results demonstrated that the white flower trait had completely disappeared in the F 1 generation.

Importantly, Mendel did not stop his experimentation there. He allowed the F 1 plants to self-fertilize and found that 705 plants in the F 2 generation had violet flowers and 224 had white flowers. This was a ratio of 3.15 violet flowers to one white flower, or approximately 3:1. When Mendel transferred pollen from a plant with violet flowers to the stigma of a plant with white flowers and vice versa, he obtained approximately the same ratio irrespective of which parent—male or female—contributed which trait. This is called a reciprocal cross —a paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross. For the other six characteristics that Mendel examined, the F 1 and F 2 generations behaved in the same way that they behaved for flower color. One of the two traits would disappear completely from the F 1 generation, only to reappear in the F 2 generation at a ratio of roughly 3:1 (Figure 3).

Upon compiling his results for many thousands of plants, Mendel concluded that the characteristics could be divided into expressed and latent traits. He called these dominant and recessive traits, respectively. Dominant traits are those that are inherited unchanged in a hybridization. Recessive traits become latent, or disappear in the offspring of a hybridization. The recessive trait does, however, reappear in the progeny of the hybrid offspring. An example of a dominant trait is the violet-colored flower trait. For this same characteristic (flower color), white-colored flowers are a recessive trait. The fact that the recessive trait reappeared in the F 2 generation meant that the traits remained separate (and were not blended) in the plants of the F 1 generation. Mendel proposed that this was because the plants possessed two copies of the trait for the flower-color characteristic, and that each parent transmitted one of their two copies to their offspring, where they came together. Moreover, the physical observation of a dominant trait could mean that the genetic composition of the organism included two dominant versions of the characteristic, or that it included one dominant and one recessive version. Conversely, the observation of a recessive trait meant that the organism lacked any dominant versions of this characteristic.

CONCEPTS IN ACTION

For an excellent review of Mendel’s experiments and to perform your own crosses and identify patterns of inheritance, visit the Mendel’s Peas web lab .

Also, check out the following video as review

• Johann Gregor Mendel, “Versuche über Pflanzenhybriden.” Verhandlungen des naturforschenden Vereines in Brünn , Bd. IV für das Jahr, 1865 Abhandlungen (1866):3–47. [for English translation, see http://www.mendelweb.org/Mendel.plain.html]

Introductory Biology: Evolutionary and Ecological Perspectives Copyright © by Various Authors - See Each Chapter Attribution is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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1865: Mendel's Peas

1865: mendel's peas.

From earliest time, people noticed the resemblance between parents and offspring, among animals and plants as well as in human families. Gregor Johann Mendel turned the study of heredity into a science.

Mendel was a monk in the Augustinian order, long interested in botany. He studied mathematics and science at the University of Vienna to become a science teacher. For eight years, starting in 1857, he studied the peas he grew in the garden of his monastery. He carefully pollinated the plants, saved seeds to plant separately, and analyzed the succeeding generations.

He self-pollinated plants until they bred true - giving rise to similar characteristics generation after generation. He studied easily distinguishable characteristics like the color and texture of the peas, the color of the pea pods and flowers, and the height of the plants.

When he crossed true-breeding lines with each other, he noticed that the characteristics of the offspring consistently showed a three to one ratio in the second generation. For example, for approximately every three tall plants, one would be short; for about every three plants with yellow peas, one would have green peas. Further breeding showed that some traits are dominant (like tall or yellow) and others recessive (like short or green). In other words, some traits can mask others. But the traits don't blend: they are inherited from the parents as discrete units and remain distinct. Furthermore, different traits - like height and seed color - are inherited independently of each other.

More Information

References:.

Mendel read his paper, "Experiments in Plant Hybridization" at meetings on February 8 and March 8, 1865. He published papers in 1865 and 1869 in the Transactions of the Brunn Natural History Society .

Some Biographies of Mendel:

Iltis, Hugo, Life of Mendel . Eden and Cedar Paul, trans. London: George Allen & Unwin Ltd. 1932. From the German publication, "Gregor Johann Mendel, Leben, Werk, und Wirkung", Berlin: Julius Springer, 1924.

Orel, Vitezslav, Gregor Mendel: The First Geneticist . Oxford & London: Oxford University Press, 1996.

In the following paper, scientists explained, in molecular detail, the cause of the wrinkled seed trait that Mendel had observed in his peas:

Bhattacharyya M.K., Smith A.M., Ellis T.H., Hedley C., and Martin C.. The wrinkled-seed character of pea described by Mendel is caused by a transposon-like insertion in a gene encoding starch-branding enzyme. Cell , 60: 115-122, 1990.

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Last updated: April 22, 2013

NOTIFICATIONS

Mendel’s experiments.

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Mendel is known as the father of genetics because of his ground-breaking work on inheritance in pea plants 150 years ago.

Gregor Johann Mendel was a monk and teacher with interests in astronomy and plant breeding. He was born in 1822, and at 21, he joined a monastery in Brünn (now in the Czech Republic). The monastery had a botanical garden and library and was a centre for science, religion and culture . In 1856, Mendel began a series of experiments at the monastery to find out how traits are passed from generation to generation. At the time, it was thought that parents’ traits were blended together in their progeny .

Studying traits in peas

Mendel studied inheritance in peas ( Pisum sativum ). He chose peas because they had been used for similar studies, are easy to grow and can be sown each year. Pea flowers contain both male and female parts, called stamen and stigma , and usually self-pollinate. Self-pollination happens before the flowers open, so progeny are produced from a single plant.

Peas can also be cross-pollinated by hand, simply by opening the flower buds to remove their pollen-producing stamen (and prevent self-pollination) and dusting pollen from one plant onto the stigma of another.

Traits in pea plants

Mendel followed the inheritance of 7 traits in pea plants, and each trait had 2 forms. He identified pure-breeding pea plants that consistently showed 1 form of a trait after generations of self-pollination.

Mendel then crossed these pure-breeding lines of plants and recorded the traits of the hybrid progeny. He found that all of the first-generation (F1) hybrids looked like 1 of the parent plants. For example, all the progeny of a purple and white flower cross were purple (not pink, as blending would have predicted). However, when he allowed the hybrid plants to self-pollinate, the hidden traits would reappear in the second-generation (F2) hybrid plants.

Dominant and recessive traits

Mendel described each of the trait variants as dominant or recessive Dominant traits, like purple flower colour, appeared in the F1 hybrids, whereas recessive traits, like white flower colour, did not.

Mendel did thousands of cross-breeding experiments. His key finding was that there were 3 times as many dominant as recessive traits in F2 pea plants (3:1 ratio).

Traits are inherited independently

Mendel also experimented to see what would happen if plants with 2 or more pure-bred traits were cross-bred. He found that each trait was inherited independently of the other and produced its own 3:1 ratio. This is the principle of independent assortment.

Find out more about Mendel’s principles of inheritance .

The next generations

Mendel didn’t stop there – he continued to allow the peas to self-pollinate over several years whilst meticulously recording the characteristics of the progeny. He may have grown as many as 30,000 pea plants over 7 years.

Mendel’s findings were ignored

In 1866, Mendel published the paper Experiments in plant hybridisation ( Versuche über plflanzenhybriden ). In it, he proposed that heredity is the result of each parent passing along 1 factor for every trait. If the factor is dominant , it will be expressed in the progeny. If the factor is recessive, it will not show up but will continue to be passed along to the next generation. Each factor works independently from the others, and they do not blend.

The science community ignored the paper, possibly because it was ahead of the ideas of heredity and variation accepted at the time. In the early 1900s, 3 plant biologists finally acknowledged Mendel’s work. Unfortunately, Mendel was not around to receive the recognition as he had died in 1884.

Useful links

Download a translated version of Mendel’s 1866 paper Experiments in plant hybridisation from Electronic Scholarly Publishing.

This apple cross-pollination video shows scientists at Plant & Food Research cross-pollinating apple plants.

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Gregor Mendel: A Monk and His Peas

Kids may wrinkle their noses at peas, but scientists grant a lot more respect for the enormous role the little green legume seeds played in the history of genetics. Working in the solitude of an Austrian monastery, one 19th-century holy man managed to unravel the basic principles of heredity with just a handful of pea species that he bred and crossbred, counted and catalogued with monastic discipline. While plant and animal genes were Gregor Mendel's original focus , his ideas later made sense of our complex human workings, too, kicking off the scientific discipline of genetics .

An unconventional scientist

Today, Mendel is revered as the father of genetics, but the Austrian's work on heredity didn't initially make the kind of big splash in the science world achieved, for example, by his contemporary, Charles Darwin. Mendel wasn't a traditional scientist, however.

Gregor Johann Mendel was born July 20, 1822 in a region of Austria that’s now part of the Czech Republic. He grew up on the family farm and worked as a gardener. He also studied beekeeping. Despite working for a time as a primary and secondary school teacher and studying at the University of Vienna, Mendel was first and foremost a full-time monk. Mendel lived at the Augustinian Abbey of Brno (then part of the Austro-Hungarian Empire) from 1843 until his death in 1884, acting as its revered Abbott for more than half of those years.

When Mendel began his experiments on the pea plants of the monastery garden in 1856, at first merely to develop new color variants and then to examine the effects of hybridization, it was independent of any university and well outside of the public eye.

Some genes are bossier

In the 19th century, it was commonly believed that traits — whether plant, animal or human — were passed on to offspring in a blend of characteristics "donated" by each parent. Heredity was a poorly understood in general, and the concept of a gene did not exist at all.

It was in this scientific environment that Mendel set out to study 34 subspecies of the common garden pea, a vegetable noted for its many variations in color, length, flower, leaves and for the way each variation appears clearly defined. Over eight years, he isolated each pea trait one at a time and crossbred species to note what traits were passed on and what traits weren't from one generation to the next.

Mendel's meticulous study produced astonishing results: Not only did the monk discover the idea of dominant and recessive traits, he was able to apply a consistent mathematical formula that explained the frequency with which each trait appeared. His discoveries would be summarized into some basic principles:

• That each inherited trait is determined by units (what we'd later call a gene) passed on independently of other traits.
• That each trait is made up of two units, one received from each parent.
• That though one unit of a trait may be inherited but not expressed in the individual, that "hidden" trait can still be passed on to successive generations.

Mendel gets his due eventually

The importance of Mendel's work wouldn't be recognized for another 40 years, well after his death. The monk's relative obscurity in scientific circles meant that few institutions took notice of his original published results. His forgotten papers resurfaced only after further work in genetics began to make some sense of his then-unconventional theories.

The chromosome theory of inheritance, or the idea that we receive a combination of traits from each parent carried on a set of distinct pairs, was proposed in 1902 and was the first study to rely heavily on Mendel's ideas of dominant and recessive traits.

When Mendel's principles were fully incorporated in the early 20th century, genetics really took off.

By 1909, a handful of funny-sounding names such as alleles, zygotes and others were finally pinned to the things Mendel had first described in his humble experiments, and scientists launched into a century-long frenzy to explain how all of our biological quirks and quarks came to be.

This article, adapted and updated, was originally part of a LiveScience series about People and Inventions that Changed the World .

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• 19 July 2022

The true legacy of Gregor Mendel: careful, rigorous and humble science

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Mendel showed that flower colour in pea plants can be inherited. The flower in the centre is a cross between the pink flower and the white flower. Credit: Oxford Science Archive/Print Collector/Getty

Genetics is fiendishly complex. We know this from decades of molecular biology, from the resulting studies on the sequencing and analysis of genomes and from our increasing knowledge of how genes interact with the environment. So how did the Augustinian friar, teacher and citizen scientist Gregor Mendel manage to describe principles of inheritance that still stand today — from work he performed alone in his monastery garden in the 1850s and 1860s?

Many of the details have been lost to history, because notes of Mendel’s experiments, including his interim observations and his working methods, were burnt after his death, as Kim Nasmyth at the University of Oxford, UK, describes in a Perspective article in Nature Reviews Genetics 1 .

But from his published works, as well as historical sources that have recently come to light, it’s clear that Mendel was a careful scientist; cautious, patient and committed to data. These qualities allowed him to make discoveries that have stood the test of time. The 200th anniversary of his birth on 22 July 1822 provides an opportunity to celebrate and recognize a giant in science. “Viewed in the light of what was known of cells in the mid-nineteenth century, Mendel was decades ahead of his time,” write Peter van Dijk at KeyGene in Wageningen, the Netherlands, and his colleagues in a Perspective article in Nature Genetics 2 .

Model communication

Although Mendel had no knowledge of genes, chromosomes or genomes, he laid the foundations for genetics in a paper, ‘Experiments on plant hybrids’, which he presented to the Natural History Society of Brno (now in the Czech Republic) in 1865 3 . Starting with 22 plants of the garden pea, Pisum sativum , and using manual pollination, Mendel crossbred these specimens and their progeny multiple times, producing more than 10,000 plants over 8 years. Plants from each pollination cycle were classified according to various characteristics, such as the colour and shape of the seeds and the position of flowers. By analysing these data, Mendel discovered that certain traits — shape and colour, for example — can be passed down from one generation to the next.

How did Mendel arrive at his discoveries?

The paper is a model for research communication. It describes, in accessible language, how Mendel established controls and protected the integrity of his experiments (such as taking steps to reduce the risk of wind-blown or insect pollination). He is generous in crediting others’ work on the subject. The final part of the manuscript includes a discussion of caveats and potential sources of error. “The validity of the set of laws suggested for Pisum requires additional confirmation and thus a repetition of at least the more important experiments would be desirable,” Mendel writes in the conclusion.

Although in his paper he did coin the terms ‘dominant’ and ‘recessive’ — which remain fundamental concepts in genetics today — Mendel’s caution in interpreting his results proved well-founded. Generations of geneticists and molecular and structural biologists have since demonstrated that observable characteristics do not result from genes alone. By working with model organisms and studying familial diseases and human populations, scientists have shown time and again that characteristics are influenced by an intricate interplay between a host of factors. These include RNA, epigenetics (chemical alterations to DNA bases that don’t change the DNA sequence), the position of a gene within both the genome and the nucleus of a cell, and how all of the above interact with environmental factors.

A statue of Gregor Mendel in the Abbey of St Thomas in Brno, Czech Republic, where Mendel was abbot. Credit: Alamy

And yet, as has been well documented, Mendel’s name was wrongly and irresponsibly appropriated to give weight to eugenics, the scientifically inaccurate idea that humans can be improved through selective breeding. Just a few decades after his death in 1884, his work began to be discussed and cited by scientists advocating theories of racial superiority. That shadow of scientific racism — in which research and evidence are distorted to cause harm — still stalks science today.

Genetics, along with palaeontology, has gone on to provide extraordinarily precise tools for understanding human origins. Genetics has also revealed that there is more genetic variation between people in the same racial category than there is between people from different races, illustrating that there is no biological basis for what we call race. Genetics still holds many secrets, including the role of genes in human behaviour. But we now know that genes are not destiny, four words that bear repeating loudly and frequently.

In laying the foundations of genetics, Mendel set an example in his patient and comprehensive approach to collecting data. In science’s current age of hyper-competitiveness, it is worth pausing for just a moment to celebrate his absolute commitment to careful observation, rigour in analysis and humility in interpreting the results.

Nature 607 , 421-422 (2022)

doi: https://doi.org/10.1038/d41586-022-01953-z

Editor’s note: There is scholarly debate on Mendel’s date of birth. According to historians, Mendel and his family celebrated on 22 July, and many surviving documents also point to this date. However, there is also evidence for 20 July, which is the date for the official 200th anniversary commemoration.

Nasmyth, K. Nature Rev. Genet. 23 , 447–452 (2022).

Article   PubMed   Google Scholar  

van Dijk, P. J., Jessop, A. P. & Ellis, T. H. N. Nature Genet. 54 , 926–933 (2022).

Mendel, G. Verh. Ver. Brünn 4, 3–47 (1866).

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"Experiments in Plant Hybridization" (1866), by Johann Gregor Mendel

During the mid-nineteenth century, Johann Gregor Mendel experimented with pea plants to develop a theory of inheritance. In 1843, while a monk in the Augustian St Thomas’s Abbey in Brünn, Austria, now Brno, Czech Repubic, Mendel examined the physical appearance of the abbey’s pea plants ( Pisum sativum ) and noted inconsistencies between what he saw and what the blending theory of inheritance, a primary model of inheritance at the time, predicted. With his experiments, which he recored in “Versuche über Pflanzenhybriden” (“Experiments in Plant Hybridization”) in 1865, Mendel discredited the blending theory of inheritance, and from them he proposed laws for inheritance patterns. Despite the fact that Mendel’s work did not define all aspects of inheritance, his ideas and laws contributed to later concepts of traits, specifically that offspring inherit traits from their parents via genes, that an offspring has at least two genetic factors for any given qualitative trait, and that the offspring inherits the genetic factors in equal proportion from both parents.

In 1856 Mendel noticed that plants in the same species had different physical appearances, including colors, heights, and seed shapes. At the time, many biologists held that all offspring were a mixture of parental traits that could never be separated back into the original parental traits. Consequently, all traits would eventually blend together and result in a homogenous amalgamation of the parental characters. This idea of a blended inheritance conflicted with what Mendel noted in many of the abbey’s plants. Mendel investigated these phenomena by experimentally mating pea plants and observing the results.

Mendel encountered a number of benefits in using the pea plant for his experiments on heredity. Specifically, the Pisum sativum plant reproduces and matures quickly, has easily observable physical traits, and can be easily artificially fertilized. As Mendel sought to trace the heredity of physical characteristic’s through generations, he needed to fertilize plants from one generation with others from the same generation. With controlled fertilization, Mendel bred generations of pea plants with the confidence that there was little or no contamination from plants of other generations. Mendel managed mating by removing the reproductive organ of a flower (piston) from one plant and pollinating another plant of his choice. He repeated his tests with thousands of plants in a relatively short time.

Mendel used pea plants that, within a lineage, displayed only one physical characteristic, like a specific pod color or a specific seed shape, for many generations. He then crossed those plants with those from a different lineage that had displayed a different physical characteristic for many generations. He chose to cross pea plants with seven different characteristics: plant height (tall vs. short), seed color (green vs. yellow), seed shape (smooth vs. wrinkled), seed-coat color (gray vs. white), pod shape (full vs. constricted), pod color (green vs. yellow), and flower distribution (along stem vs. at the end of the stem). Mendel examined the first offspring generation, noted physical appearances and then crossed plants within the first generation to produce a second generation of offspring. By examining each characteristic throughout the generations of offspring, Mendel concluded that individuals in successive generations displayed the original characteristics of their parents.

Mendel noticed that only one of the characteristics for each category was displayed per offspring. For example, pea plants exhibited either green or yellow seeds, but not both colors within the same plant or seed colors that blended yellow and green. In the first generation of hybrids the trait that resulted always mirrored one of the parents. These results discredited the theory of blending between parental traits, as the offspring of a tall pea plant and a short pea plant yielded not a medium pea plant, but only tall pea plants.

From 1856 to 1863, Mendel continued his experiments and noted that the trait of the parent that was missing in an organism from the first generation reappeared in organisms of the second generation. Furthermore, the ratio of these traits within the second generation occurred in roughly a 3:1 proportion, such that out of every four offspring, approximately three possessed the physical trait of one parent and one displayed the physical trait of the other parent. The trait that appeared most often Mendel called the dominant trait, and the other he called recessive. Through his experiments, Mendel determined the dominant traits in pea plants to be: tall plant height, yellow seed color, smooth seed shape, gray seed-coat color, full pod shape, green pod color, and flower distribution along the stem.

Mendel re-tested his experiment from 1856 to 1863 on almost 30,000 plants to verify his results. He proposed that factors (later called genes) determine the appearance of a characteristic and that for each physical character, a factor has two contributing forms (later called alleles). Furthermore, an organism inherits one form from its mother and one form from its father. If, within a factor, the forms are different, for example, a green seed color form via the mother and a yellow seed color form via the father, then one is dominant and determines the physical appearance of a trait in an offspring, while the other is recessive, and doesn’t influence the physical character. Mendel formulated a theory of particulate inheritance around this theory that recessive traits, although not always physically expressed in the offspring of one generation, can reappear in the offspring of subsequent generations. Mendel postulated two laws to explain the results he had obtained.

The law of segregation states that during sex cell formation, each sex cell will receive one factor out of a pair of factors. The law of independent assortment, claims that when each of these sex cells receives a factor, the members of each pair separate into sex cells independently of one another.

Few people noticed Mendel’s experiments for most of the nineteenth century, even after publication of “Versuche über Pflanzenhybriden” in the journal Verhandlungen des naturforschenden Vereins Brünn (Proceedings of the Natural History Society of Brünn) in 1866. Mendel’s article remained untranslated from German. However, Mendel posthumously received credit for his work. In 1899 at the Royal Horticultural Society’s International Conference on Hybridization and Plant Breeding in London, Great Britain, William Bateson revived the papers and findings of Mendel through his own experiments on heredity in the UK.

Furthermore, in 1900, three botanists in Europe, Hugo de Vries, Carl Correns, and Erich von Tschermak-Seysenegg, each performed their own experiments and independently arrived at the same conclusions as Mendel, without knowing Mendel’s work. Repetitions of Mendel’s experiments showed that not all traits exhibited a classic dominance and recessive character. Hybrids, or mixes, appeared and showed that a blending of traits can occur in some cases.

• Corcos, Alain F. and Floyd V Monaghan. Gregor Mendel’s Experiments on Plant Hybrids: A Guided Study . New Brunswick, NJ: Rutgers University Press, 1993.
• Dodson, Edward O. “Mendel and the Rediscovery of His Work.” The Scientific Monthly 81 (1955): 187–95.
• Hartl, Daniel L. and Vitezslav Orel. “What Did Gregor Mendel Think He Discovered?” Genetics 131 (1992): 245–53.
• Iltis, Hugo. “Gregor Mendel and His Work.” The Scientific Monthly 56 (1943): 414–23.
• Mendel, Gregor Johann. “Versuche über Pflanzen-Hybriden” [Experiments Concerning Plant Hybrids]” [1866]. In Verhandlungen des naturforschenden Vereines in Brünn [Proceedings of the Natural History Society of Brünn] IV (1865): 3–47. Reprinted in Fundamenta Genetica , ed. Jaroslav Kříženecký, 15–56. Prague: Czech Academy of Sciences, 1966. http://www.mendelweb.org/Mendel.html

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Science News

How we got from gregor mendel’s pea plants to modern genetics.

Philosopher Yafeng Shan explains how today's understanding of inheritance emerged from a muddle of ideas

In 1900, Gregor Mendel’s experiments on pea plants were introduced into the study of heredity.

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By Elizabeth Quill

February 7, 2022 at 11:00 am

The year was 1900. Three European botanists — one Dutch, one German and one Austrian — all reported results from breeding experiments in plants. Each claimed that they had independently discovered some remarkable patterns in inheritance that had been noticed by Gregor Mendel decades earlier and reported in “Versuche über Pflanzen-Hybriden,” or “Experiments in Plant Hybridization.” All three relied on or built upon the work of the Austrian monk, whose experiments in pea plants are famous today as the foundation of genetics.

Yet at the time, “there was no such discipline as genetics, nor was there a concept of the gene,” says Yafeng Shan, a philosopher of science at the University of Kent in England. Instead, there were many theories of how traits were inherited, including Charles Darwin’s theory of pangenesis, which described particles of inheritance called “gemmules” thought to be given off by all cells in the body and to collect in the reproductive organs.

From the muddle of ideas, Shan says, those three reports at the dawn of the 20th century helped introduce Mendel’s work to other scientists in the fledgling field of heredity. That set the stage for the development of Mendelian genetics as we know it today, and no doubt played into a century’s worth of developments in molecular biology, from the discovery of the structure of DNA to the sequencing of the human genome and the rise of genetic engineering.

To celebrate our 100th anniversary, we’re highlighting some of the biggest advances in science over the last century. To see more from the series, visit Century of Science .

But the path to our current understanding of the inheritance and variation at the heart of modern biology has been far more winding than most biology textbooks reveal. In the conversation that follows, Elizabeth Quill, special projects editor at Science News , talks with Shan about the origins of genetics and what progress over the past century tells us about the nature of science.

Quill: Our understanding of genetics has emerged nearly entirely in the last century. Can you take us back? What did scientists know at the beginning of the century?

Shan: The term genetics was coined to describe the study of heredity in 1905 by the English biologist William Bateson in a letter to his friend. The term gene was introduced later, in 1909, by the Danish biologist Wilhelm Johannsen to refer to the unit of hereditary material.

That said, there were at least 30 different theories of heredity or inheritance at the beginning of the 20th century. So to borrow Charles Dickens’ phrase: It was the best of times, and it was the worst of times for the study of heredity. There were many different theories, methods and lines of inquiry available, but there was no consensus on the mechanism and patterns of inheritance, nor was there any consensus on a reliable way to study them.

Quill: In biology classes, we learn that Gregor Mendel’s experiments breeding pea plants in the mid-19th century taught us that inherited traits are delivered to offspring on pairs of genes, one from each parent, and that there are dominant and recessive forms of genes. But if the concept of gene wasn’t fully developed in Mendel’s day, what did his work actually reveal?

Shan: If you walk into any university library and pick up a copy of a genetics textbook today, you may find the following narrative: Mendel developed a theory of inheritance, but unfortunately, the theory was neglected or overlooked for over three decades, and only rediscovered in 1900.

Actually, there are mistakes in that: Mendel’s theory was not a theory of inheritance. He never used the German word for heredity — Vererbung . His concern was instead about the development of hybrids. In other words, Mendel did propose a theory for patterns of characteristics in plant hybrids, but it is not a theory of inheritance. And Mendel’s theory was not neglected or overlooked. There were more than a dozen citations to his paper before 1900. That’s not a lot, but definitely not overlooked.

Some fascinating things did happen in 1900, though. Mendel’s work was introduced to the study of heredity by Hugo de Vries, Carl Correns and Erich von Tschermak. All of them renewed Mendel’s work for different purposes. That being said, none of these three became a pioneer of Mendelism as we know it today.

Quill: Who was that pioneer?

Shan: After the introduction of Mendel’s work to the study of heredity, one important pioneer was William Bateson, an English biologist. Originally, he was not interested in the problem of heredity. So, to some extent, he was an outsider. He was studying evolution, but he found Mendel’s work useful. Based on Mendel’s findings, he said, we can develop a new theory that is the correct way to study heredity and will further shed light on the nature of evolution. He was one of the most prominent figures in the movement, which at first was resisted by many people.

To cut the story short, Mendelism won the victory — though in the early days, it was quite different from the Mendelian genetics of today, which was mainly established and developed by T.H. Morgan and his students and team at Columbia.

Quill: Thomas H. Morgan isn’t as widely known as Mendel or Darwin, for example. Why was his work so important and what made it different from what came before?

Shan: He may not have become a household name, but Morgan is considered one of the most influential geneticists ever. He actually began his career as a zoologist and had diverse interests in morphology, regeneration, embryology, et cetera. He was using fruit flies as experimental organisms to test the Darwinian theory of evolution. Darwin believed evolution happened through a series of minor and gradual changes. Others, including de Vries, believed species evolved through mutations: radical, sudden change. Morgan bought that argument.

Initially, his work was not very successful, in his own words. He started his experiment in 1908 and found nothing at all until 1910. He mentioned to an office friend that it was two years’ time, just wasted. But sometimes magical things just happen. After two years, he was surprised to find a mutation.

But he was puzzled. This mutation that he observed could not be explained by de Vries’ theory of mutation. Rather, it could be better accounted for by the Mendelian approach. So here is where Morgan and his team began developing a Mendelian approach.

What Morgan did differently from early Mendelians, say Bateson, was that he and his team incorporated Mendelism with another important line of inquiry in the field, the chromosome theory of inheritance, which was developed primarily by American geneticist Walter Sutton and German zoologist Theodor Boveri. They came up with the idea that hereditary material must be somewhere within the chromosomes. That provided a physical basis for hereditary material.

Quill: And that must have proved successful?

Shan: Combining Mendelism and the chromosome theory of inheritance leads to one of the most remarkable achievements of Morgan and his colleagues: They produced the chromosome map for the fruit fly. They located different genes at different locations on the chromosome. With that map, you can calculate the frequency of recombination of genes in the following generations. With that single map, you can identify not only the position of the genes on the chromosomes, but also predict the phenomenon of inheritance.

Quill: We haven’t yet talked about DNA. Were geneticists interested in DNA at that time?

Shan: The study of DNA was part of the job of biochemists. DNA was first identified in the mid-19th century, roughly the same time as when Mendel was working on his peas. Swiss chemist Friedrich Miescher was looking for the most fundamental constituents of life. He identified some substance coming from the nucleus of the cell and named it “nuclein.” That is what we now call DNA.

After his great discovery, the importance of and implications of nuclein, or DNA, were debated for decades. By the turn of the 20th century, nuclein was identified as a nucleic acid, and the five bases of nucleic acids — G, A, C, T and U — were also identified. In the 1920s and ’30s, biochemists came to know that the nucleic acid present in chromosomes is DNA.

But the makeup of DNA was only being pursued by biochemists. Those who studied the problem of heredity did not pay serious attention to DNA until the 1940s.

Quill: How did DNA get incorporated into the study of heredity?

Shan: That is the process of merging of the two lines of inquiry — the line of inquiry in genetics and the line of inquiry in biochemistry. For geneticists, their main concern was about a pattern and mechanism of inheritance and how a particular trait is transmitted from generation to generation. And on the other hand, biochemists were looking for the physical foundations of life.

With the success of T.H. Morgan and his colleagues, geneticists had a better capacity to predict and explain the patterns of inheritance. Then an immediate question arose: So, what are genes?

According to the Morgan school of classical genetics, a gene is just a segment of the chromosome. That’s very easy. There was very popular analogy in which they described genes as beads on the string. But it was still quite unclear what the physical basis was.  

Oswald Avery and his colleagues reported evidence in 1944 that DNA, rather than protein, carries hereditary information. Even though Avery’s experiment was not actually the first — it was confirming work done by others in 1939 — his work was better received and better known within the community. People often refer to Avery’s great experiment, though at the time some skepticism remained.

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Quill: That background helps explain why the discovery of the double-helix structure of DNA, from James Watson and Francis Crick, along with Rosalind Franklin and Maurice Wilkins, was so monumental. By knowing the structure of DNA, people could think about how the physical process of inheritance might work. Is that right?

Shan: Today we say, ‘Ah, so the process of inheritance is quite straightforward: Basically, DNA can be transcribed to RNA, and RNA can be translated into protein, and protein is responsible for phenotypic traits.’ Roughly speaking, it is like that.

That double-helix model provided a very reliable and useful framework to study DNA replication, and transcription. That’s crucially important for the later work in molecular genetics. At the time, in 1953, when Watson and Crick proposed that model, their work was not immediately well-received. It was not cited a lot — just like Mendel’s paper — until the end of the 1950s, when other work confirmed that the structure of DNA provides a mechanism of controlling protein synthesis.

There are quite a lot of important discoveries that followed. It’s probably unfair, but from my point of view, the others aren’t as exciting as the discovery of the double helix. If I can borrow a phrase from American philosopher Thomas Kuhn, we are now in the period of “normal science,” or what he calls “mopping up.” It took another 40 or 50 years to get where we are now, but in terms of milestones in the history of genetics, if you ask me if there’s anything as important as the introduction of Mendel’s work and the discovery of the double helix, I would say I’m afraid nothing else is as fascinating.

Quill: Looking back at the history of genetics, are there lessons to take away in how we think about science and scientific progress?

Shan: When we look back, we see that genetics developed through multiple parallel lines from the very beginning. We’ve got Darwin. We’ve got de Vries developing Darwin’s approach. We’ve got Francis Galton and his biometric approach, developed further by Karl Pearson and Raphael Weldon — which we didn’t even get to discuss. We’ve got Bateson borrowing ideas from Mendel. And there is also the important line of inquiry, the chromosome theory, independently developed primarily by Sutton and Boveri.  

Across the century, we start from classical genetics, then molecular genetics and now epigenetics (which studies changes in an organism that result from how genes are turned on and off, rather than alterations to the DNA sequence). That’s three historical episodes. One popular interpretation is that these three historical episodes or paradigms can be viewed as three scientific revolutions. But these paradigms are interactive with each other, not destructive or revolutionary. For instance, molecular genetics arises from the need to better understand the physical basis of heredity in classical genetics. Even today, the methods of classical genetics are still used in some problems.

I think there are lessons here about the nature and the aim of science. Science seems to be often characterized as an enterprise in explaining or understanding the phenomena of the world. It’s right to say scientists do make efforts to explain and understand. But there is another essential feature of science, namely exploratory or investigative. From the very beginning, none of the geneticists of the past century probably had a very clear idea of what a good explanation, what a good theory, what a good experiment would look like.

Our understanding of inheritance improved with the development of investigative or exploratory research. Ultimately, some of science’s most important features cannot be simply captured by concepts like truth or knowledge or understanding.

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Gregor Mendel, Priest and Scientist

Gregor Mendel of Austria (1882-1884) was a young priest in the Augustinian Abbey of St. Thomas in Brno, Austria, who in his spare time he studied in his monastery garden the reproductive patterns of the garden pea. From these studies Mendel was able to determine certain laws at work which determine the inheritance of dominant and recessive character traits. Much of his later work required sitting at a brass microscope for hours on end until at one point he began to suffer from eye strain. As he complained in a letter to a friend, “Since ordinary dispersed daylight was insufficient for my work on the tiny Hieracium flowers, I made use of an illuminating apparatus, without thinking what damage I might do to my eyesight.”

Mendel eventually published in a relatively obscure journal several essays summarizing the mathematical  laws of inherited dominant and recessive traits. As a result of his efforts, today Mendel is regarded as the founder of the science called genetics ( the term was coined by William Bateson).

As with almost anyone who discovers a new science, at first Mendel’s work was largely ignored and did not finally gain the respect of the scientific community until sixteen years after his death. However, upon the rediscovery of his work by Bateson and others in 1900, the enormous significance of his studies had one of his early admirers declaring Mendel’s experiments worthy to rank with the atomic laws of chemistry, while another enthusiast declared Mendel’s laws to be no less important than those of a Newton or a Dalton.

Since the first publication of his ideas thirty-five years earlier, Mendel’s Laws had suffered an eclipse of scientific interest for two reasons. First, Charles Darwin’s theory of evolution seemed, by its emphasis on random variations in reproduction, to deny the existence of “laws” regarding inherited traits. In the scientific community the excitement aroused by Darwin’s theory made unlikely the chance that Mendel could be taken seriously. Darwin himself seems never to have been aware of Mendel’s groundbreaking discoveries. The “randomness” of Darwin’s theory seemed to push many toward the inference that God is not needed to explain the complex orchestration of Nature. Mendel’s genetics would have pushed randomness aside and restored the idea of order in nature just when biologists were getting comfortable with Darwin. Perhaps one of the great misfortunes in the history of science is that Darwin and Mendel never got together to compare notes.

The second reason for the general neglect of Mendel’s work is that he himself failed to develop further his complex theories or to vigorously promote them in the scientific community. At the age of 45 he was elected abbot of his own monastery, and was consumed for many years with administrative duties which blocked the pursuit of the research that had meant so much to him in his youth. Add to these distractions an endless and exhausting battle with the government over the new monastery tax that Mendel regarded as unconstitutional. Abbot Mendel was often heard by other monks to express regret at his lost opportunity to advance his unfinished scientific work. These complaints would often be followed by the exclamation, “My time will surely come.”

And come it surely has.

The science of genetics has grown far beyond what Mendel could have imagined in his day. In 1952 researchers discovered that DNA – deoxyribonucleic acid – was the molecule that controlled inheritance. Within a year Watson and Crick had cracked the genetic code of DNA. Because cancer is a genetic disease, it will now be possible to combat cancer by learning more about how and why cancer kills. Through the science of genetics great advances in law enforcement also have been made possible by lab technicians being able to match samples of blood, hair, and sperm with those of criminal suspects.

Today Mendel’s cemetery stone is so mold-covered his name carved on it can hardly be read. Not an impressive monument, yet he yearned for a greater one, as we can see from these prophetic lines of a poem he wrote in his youth:

  The highest goal of earthly ecstasy,

That of seeing, when I arise from the tomb,

My art thriving peacefully

Among those who are to come after me.

• Biology Article
• Mendel Laws Of Inheritance

Mendel's Laws of Inheritance

Inheritance can be defined as the process of how a child receives genetic information from the parent. The whole process of heredity is dependent upon inheritance and it is the reason that the offsprings are similar to the parents. This simply means that due to inheritance, the members of the same family possess similar characteristics.

It was only during the mid 19th century that people started to understand inheritance in a proper way. This understanding of inheritance was made possible by a scientist named Gregor Mendel, who formulated certain laws to understand inheritance known as Mendel’s laws of inheritance.

Table of Contents

Mendel’s Laws of Inheritance

Why was pea plant selected for mendel’s experiments, mendel’s experiments, conclusions from mendel’s experiments, mendel’s laws, key points on mendel’s laws.

Between 1856-1863, Mendel conducted the hybridization experiments on the garden peas. During that period, he chose some distinct characteristics of the peas and conducted some cross-pollination/ artificial pollination on the pea lines that showed stable trait inheritance and underwent continuous self-pollination. Such pea lines are called true-breeding pea lines.

Also Refer:   Mendel’s Laws of Inheritance: Mendel’s Contribution

He selected a pea plant for his experiments for the following reasons:

• The pea plant can be easily grown and maintained.
• They are naturally self-pollinating but can also be cross-pollinated.
• It is an annual plant, therefore, many generations can be studied within a short period of time.
• It has several contrasting characters.

Mendel conducted 2 main experiments to determine the laws of inheritance. These experiments were:

Monohybrid Cross

Dihybrid cross.

While experimenting, Mendel found that certain factors were always being transferred down to the offspring in a stable way. Those factors are now called genes i.e. genes can be called the units of inheritance.

Mendel experimented on a pea plant and considered 7 main contrasting traits in the plants. Then, he conducted both experiments to determine the inheritance laws. A brief explanation of the two experiments is given below.

In this experiment, Mendel took two pea plants of opposite traits (one short and one tall) and crossed them. He found the first generation offspring were tall and called it F1 progeny. Then he crossed F1 progeny and obtained both tall and short plants in the ratio 3:1. To know more about this experiment, visit Monohybrid Cross – Inheritance Of One Gene .

Mendel even conducted this experiment with other contrasting traits like green peas vs yellow peas, round vs wrinkled, etc. In all the cases, he found that the results were similar. From this, he formulated the laws of Segregation And Dominance .

In a dihybrid cross experiment, Mendel considered two traits, each having two alleles. He crossed wrinkled-green seed and round-yellow seeds and observed that all the first generation progeny (F1 progeny) were round-yellow. This meant that dominant traits were the round shape and yellow colour.

He then self-pollinated the F1 progeny and obtained 4 different traits: round-yellow, round-green, wrinkled-yellow, and wrinkled-green seeds in the ratio 9:3:3:1.

Check Dihybrid Cross and Inheritance of Two Genes to know more about this cross.

After conducting research for other traits, the results were found to be similar. From this experiment, Mendel formulated his second law of inheritance i.e. law of Independent Assortment.

• The genetic makeup of the plant is known as the genotype. On the contrary, the physical appearance of the plant is known as phenotype.
• The genes are transferred from parents to the offspring in pairs known as alleles.
• During gametogenesis when the chromosomes are halved, there is a 50% chance of one of the two alleles to fuse with the allele of the gamete of the other parent.
• When the alleles are the same, they are known as homozygous alleles and when the alleles are different they are known as heterozygous alleles.

Also Refer:   Mendelian Genetics

The two experiments lead to the formulation of Mendel’s laws known as laws of inheritance which are:

• Law of Dominance
• Law of Segregation
• Law of Independent Assortment

This is also called Mendel’s first law of inheritance. According to the law of dominance, hybrid offspring will only inherit the dominant trait in the phenotype. The alleles that are suppressed are called the recessive traits while the alleles that determine the trait are known as the dominant traits.

The law of segregation states that during the production of gametes, two copies of each hereditary factor segregate so that offspring acquire one factor from each parent. In other words, allele (alternative form of the gene) pairs segregate during the formation of gamete and re-unite randomly during fertilization. This is also known as Mendel’s third law of inheritance.

Also known as Mendel’s second law of inheritance, the law of independent assortment states that a pair of traits segregates independently of another pair during gamete formation. As the individual heredity factors assort independently, different traits get equal opportunity to occur together.

• The law of inheritance was proposed by Gregor Mendel after conducting experiments on pea plants for seven years.
• Mendel’s laws of inheritance include law of dominance, law of segregation and law of independent assortment.
• The law of segregation states that every individual possesses two alleles and only one allele is passed on to the offspring.
• The law of independent assortment states that the inheritance of one pair of genes is independent of inheritance of another pair.

Also Read:   Non-Mendelian Inheritance

Stay tuned with BYJU’S to learn more about Mendel’s Laws of Inheritance. You can also download the BYJU’S app for further reference on Mendel’s laws.

Frequently Asked Questions

What are the three laws of inheritance proposed by mendel.

The three laws of inheritance proposed by Mendel include:

Which is the universally accepted law of inheritance?

Law of segregation is the universally accepted law of inheritance. It is the only law without any exceptions. It states that each trait consists of two alleles which segregate during the formation of gametes and one allele from each parent combines during fertilization.

Why is the law of segregation known as the law of purity of gametes?

The law of segregation is known as the law of purity of gametes because a gamete carries only a recessive or a dominant allele but not both the alleles.

Why was the pea plant used in Mendel’s experiments?

Mendel picked pea plants in his experiments because the pea plant has different observable traits. It can be grown easily in large numbers and its reproduction can be manipulated. Also, pea has both male and female reproductive organs, so they can self-pollinate as well as cross-pollinate.

What was the main aim of Mendel’s experiments?

The main aim of Mendel’s experiments was:

• To determine whether the traits would always be recessive.
• Whether traits affect each other as they are inherited.
• Whether traits could be transformed by DNA.

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very nice. it is the best to study about genetics

Genetic inheritance is so interesting

It helped me a lot Thanks

It is so amazing thanks a lot

Superb, it’s interesting.

It is very useful becoz all details explain in simple manner with examples

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It helped me alot

If Mendel gave three law the what is the law of unit of characters and who proposed this law . Please clear my doubt a little bit faster , it is little important for me.

The Law of unit characters was proposed by Mendel. He explained that the inheritance of a trait is controlled by unit characters or factors, which are passed from parents to offspring through the gametes. These factors are now known as genes. Each factor exists in pairs, which are known as alleles.

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