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Rediscovery of Mendelism: Carl Correns, Erich Von Tschermak-Seysenegg, Hugo De Vries, Significance, Practice Problems and FAQs

Rediscovery of Mendelism: Carl Correns, Erich Von Tschermak-Seysenegg, Hugo De Vries, Significance, Practice Problems and FAQs

Genetics is the study of heredity and variations and we all know that Gregor Johann Mendel is the father of genetics. He was a monk from a monastery in Brunn, Austria. He was interested in natural science and did his work on the pea plant (Pisum sativum). He discovered three fundamental laws of inheritance in 1865.


                       Fig: Gregor Johann Mendel

But you know from 1865 to 1900, the discovery of Mendel was unnoticed. Can you guess, what must be the reasons behind this?.

The ideas of Mendel were ahead of his time. For example, using a Punnett square to represent the possible genotypes of an offspring arising from a particular cross was not acceptable to the scientists of that period. The communication procedure to publish a research work was not easy during that time. For example, in the absence of electronic media most of the communications in those periods was possible only through letters. These letters will reach the destination by taking time as the transporting was possible mainly through ships. Most of the scientists in that period were busy with the evaluation of Darwin's work. Many of the famous scientists of that period were not aware of the cytological basis of heredity. For example, Mendel proposed the factors as stable and discrete units that controlled the expression of traits and of the pair of alleles that did not blend with each other. But in nature continuous variation is seen. Applications of mathematical principles to explain biology were also not acceptable to most of the scientists.

But after his death, three botanists namely Hugo de Vries of Holland, Carl Correns of Germany, and Erich von Tschermak-Seysenegg of Austria rediscovered Mendel's laws independently. The conclusion of these botanists kept light on the importance of Mendel's work. Let’s discuss in detail the rediscovery of Mendel’s laws in this article.

Table of contents

  • Mendelism
  • Laws of Mendel
  • Rediscovery of mendelism
  • Carl Correns
  • Erich von Tschermak-Seysenegg
  • Hugo de Vries
  • Significance of rediscovery of mendelism
  • Practice problems
  • FAQs

Mendelism

Mendelism refers to the theoretical principles of heredity put forward by Gregor Johann Mendel based on his studies on Pisum sativum or garden pea. These are also known as Mendel's laws of heredity. Mendel published his work in 1866 in the ‘Annual Proceeding of Natural History Society of Brunn’.


           Fig: Pisum sativum (Garden pea)

Laws of Mendel

Mendel proposed that heredity is controlled by factors now called genes. He said that factors are present in the cells of the body and are transmitted to the next generation through gametes. During his studies, he put forth three laws of inheritance which are as follows:

  • Law of dominance (First law)
  • Law of segregation (Second law)
  • Law of independent assortment (Third law)

Law of dominance

The law of dominance states that “when two alternative factors or genes come together in an organism, only one of them called dominant is expressed while the other factor or gene of the pair called recessive remains unexpressed.” For example, when a cross is made between the homozygous dominant plant with yellow seeds (YY) and homozygous recessive plant with green seeds (yy), in the F1 generation only yellow seeds are produced.


                                    Fig: Production of yellow seeds in the F1 generation

Law of segregation

The law of segregation is the second law of inheritance. It is also called the purity of gametes. It states that ‘during gamete formation, pairs of alleles segregate such that each gamete receives only one allele’.

Or

“The two alternative factors or alleles of a pair representing a character are separated from each other at the time of gamete formation so that a gamete contains only one factor for the character and the paired condition is restored by the random fusion of gametes during fertilisation.”

For example, when a cross is made between the homozygous dominant plant with yellow seeds (YY) and the homozygous recessive plant with green seeds (yy), the segregation of alleles occurs in the F2 generation as shown below.


                         Fig: Segregation of alleles in the F2 generation

Law of independent assortment

According to the law of independent assortment, “the segregation of one pair of characters is independent of the other pair of characters when two pairs of traits are joined in a hybrid.”

Or

“If we consider the inheritance of two or more allele pairs at a time, their distribution in the gametes and in the subsequent generations is independent of each other.”

For example, when a cross is made between the homozygous dominant plant with yellow round seeds (YYRR) and the homozygous recessive plant with green wrinkled seeds (yyrr), the segregation of alleles in the F2 generation of dihybrid cross occurs as shown below which follows law of independent assortment.


                        Fig: Segregation of alleles in the F2 generation of dihybrid cross

Rediscovery of mendelism

In 1900, three scientists, Hugo de Vries, Carl Correns, and Erich von Tschermak-Seysenegg, rediscovered Mendel's laws. They were all studying different plant hybrids independently and came to Mendel's same conclusions concerning heredity. They expanded the basic principles of the Mendelian laws of inheritance in a more scientific way.

Carl Correns

Carl Correns was born in Germany and raised in Switzerland. In 1885, he started his study in botany at the University of Munich. His professor encouraged him to take an interest in botany and further advised him on his thesis subject. Correns began his experiments on plants to determine the pattern of inheritance in 1892. At that time, Correns knew some of the work of Mendel. The laws of heredity established by Mendel were first unknown to Correns. However, the paper's name changed in 1900 when Correns submitted his own findings for publication. The name of the paper was ‘G. Mendel's Law Concerning the Behaviour of the Progeny of Racial Hybrids’.


                          Fig: Carl Correns

The ‘redefining’ of Mendel's laws that Correns and de Vries did was the most precise. In his paper, Mendel discussed both ‘the law of independent assortment’ and the ‘law of combination of different characters.’ Mendel suggested that sex cells were produced as a result of the segregation of components. Mendel's law of segregation and Mendel's law of independent assortment were presented by Correns after reiterating Mendel's findings.

Key experiment

At the turn of the 20th century, Carl Correns carried out a large portion of the groundwork for the field of genetics. In a different model organism, he rediscovered and independently confirmed Mendel's results. Additionally, he made a significant contribution to Mendel's theories related to cytoplasmic inheritance, which showed the influence of extra-chromosomal variables on the phenotype.

He conducted research with the four o'clock plant, Mirabilis jalapa to look at apparent counter examples to Mendel's laws in the heredity of variegated (green and white mottled) leaf colour after rediscovering the laws of heredity, which can be explained with chromosomal inheritance.


          Fig: Mirabilis jalapa (Four o’clock plant)

While Mendelian traits behave regardless of the sex of the source parent, Correns discovered that leaf colour strongly depended on which parent had that particular trait. Growing hybrids of maize and peas for several generations and analysing new developments in cytology helped Correns to understand the transmission of paired characters. For example, the expected outcome for a recessive gene was white progeny when an ovule from a white stigma was pollinated with pollen from another white counterpart. All green progeny were produced when green pollen was applied to a green stigma, as would be expected from a dominant gene. But the progeny were green when green pollen fertilised a white stigma.

Erich von Tschermak-Seysenegg

Austria's Vienna is the birthplace of Erich von Tschermak-Seysenegg. His maternal grandfather was the renowned botanist Eduard Fenzl, who at one point tutored Gregor Mendel, and his father was a well-known mineralogist. He worked on a farm to get real-world agricultural experience while pursuing his agricultural studies at the University of Vienna. From Halle-Wittenberg University, Tschermak received a doctorate.


        Fig: Erich von Tschermak-Seysenegg

He began conducting pea-based plant breeding experiments in 1898, and by 1900, he had documented his findings.

 
           Fig: Pisum sativum (Garden pea)

Tschermak independently derived ‘Mendelian principles of heredity’ from his research on plants, just like de Vries and Correns. Tschermak was concerned about whether his paper would be accepted in comparison with those of de Vries and Correns because he was younger and less well-known in the scientific world. He was able to publish his paper quickly though, and as one of the co-discoverers of Mendel's rules, he received his share of the credit. Tschermak was a plant breeder, and he conducted hybridisation studies with the goal of enhancing crops by utilising the principles of heredity. He produced high-yielding food crops including wheat, barley, and oats, and did the majority of the work himself. He developed new disease-resistant crops, including wheat-rye and oat hybrids.

Hugo de Vries

Haarlem in the Netherlands is where Hugo de Vries was born. In 1880, he started his genetic research with plants while serving as a professor at the University of Amsterdam. Most of his hybridisation studies were conducted without him being aware of Mendel's research. De Vries came to the same findings as Mendel based on his own research. Initially published in French and then in German, De Vries' work was released in 1900. Mendel was not mentioned in the French publication, but de Vries corrected this in the German publication. Before publishing his own paper, de Vries may have read Mendel's work, and upon realising that other people were aware of Mendel's work, he may have decided to incorporate Mendel's name in the later printing.


                    Fig: Hugo de Vries

Key experiment

In the 1890s, De Vries experimented with creating hybridised variations of various plant species. He mainly worked on the plant evening Primrose or Oenothera lamarckiana. De Vries, who was not familiar with Mendel's work, employed the law of dominance, law of segregation, and law of independent assortment to explain the second generation's 3:1 ratio of phenotypes. His findings also supported his theory that certain traits are passed down through particles in organisms.


             Fig: Evening Primrose or Oenothera lamarckiana

He said that genes might cross species boundaries, with the same gene possibly being in charge of hairiness in two distinct species of flower. De Vries intended a physical cross between species, even if it is generally true that orthologous genes (a particular class of homologous genes), acquired from a common ancestor of both species, tend to stay responsible for similar traits.

De Vries changed parts of his vocabulary to fit Mendel's obscure study from thirty years earlier after learning about it in the late 1890s. He failed to cite Mendel's work when he published the findings of his tests in the French journal in 1900, but after Carl Correns objected, he acknowledged Mendel's precedence.

Significance of rediscovery of mendelism

The following are the major significances of mendelism:

  • Rediscovery of mendelism helped in expanding the awareness of the Mendelian laws of inheritance in the scientific world.
  • The basic principles of the Mendelian laws of inheritance have been explained in a more scientific way.
  • It led to the development of new experimental methods.
  • It led to the establishment of a new field of biology called Genetics.
  • Mechanism of cytological inheritance gains importance.
  • It led to the development of hybrid varieties.
  • It explains how a trait is inherited.
  • It is helpful in hybridisation studies to create novel combinations of traits.

Practice Problems

1.) Identify the odd one out.Hugo de Vries
a) Carl Correns
b) Erich von Tschermak-Seysenegg
c) Charles Darwin

Solution: A generation after Mendel published his papers, Hugo DeVries, Carl Correns, and Erich von Tschermak-Seysenegg, each independently rediscovered Mendel's work in the same year. They contributed to raising awareness of Laws of Mendelian inheritance in the scientific community. Charles Darwin was an evolutionary biologist not a co-discoverer of mendelism. He proposed the theory of natural selection. Hence, the correct option is d.

2. What would have caused Mendel's work to go unappreciated before it was rediscovered?
Answer:
Gregor Johann Mendel is the father of genetics. He was a monk from a monastery in Brunn, Austria. He was interested in natural science and did his work on the pea plant (Pisum sativum). He discovered three fundamental laws of inheritance in 1865. His work went unnoticed because of the following reasons:

  • The ideas of Mendel were ahead of his time. For example, using a Punnett square to represent the possible genotypes of an offspring arising from a particular cross was not acceptable to the scientists of that period.
  • The communication procedure to publish a research work was not easy during that time. For example, in the absence of electronic media most of the communications in those periods was possible only through letters. These letters will reach the destination by taking time as the transporting was possible mainly through ships.
  • Most of the scientists in that period were busy with the evaluation of Darwin's work.
  • Many of the famous scientists of that period were not aware of the cytological basis of heredity. For example, Mendel proposed the factors as stable and discrete units that controlled the expression of traits and of the pair of alleles that did not blend with each other. But in nature continuous variation is seen.
  • Applications of mathematical principles to explain biology were also not acceptable to most of the scientists.
  • Mendel was supposedly a monk who worked by himself in an isolated scientific environment.
  • The limited distribution of his work and the lack of self-promotion.
     

3. Why are the laws of Mendel important?
Answer:
Mendel's laws are significant because they aid in figuring out how a trait is inherited and are helpful in hybridisation studies to create novel combinations of traits.

4. Why is Mendel recognised as the ‘Father of Genetics’?
Answer
: Mendel was the first to develop the fundamental rules of heredity and provide a scientific explanation for the method of character transmission. So he is appropriately referred to as the ‘father of genetics.’

FAQs

  1. Why was not Mendel's law recognised at the time?

Answer: For the purpose of interpreting the findings, he applied mathematical logic and statistical techniques. Most scientists at the time were unfamiliar with these methods.

  1. Which laws of inheritance were followed by Carl Correns?

Answer: Mendel's law of segregation and Mendel's law of independent assortment were followed mainly by Correns.

  1. What theory did Hugo de Vries find?

Answer: Hugo de Vries discovered the mutation theory of inheritance. According to mutation theory, gene alterations in living things can have a significant impact on the organism.

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