Mendel-The Father of Genetics and His Laws of Inheritance: How is genetic information transmitted between generations? Today, we know that many traits run in families, from hair colour to height, facial features to the risk of diabetes. These all are influenced by genes, and the credit for our present understanding of heredity goes to Austrian monk Gregor Johann Mendel. He was a monk and a teacher by profession. He had a keen interest in natural science and exceptional observational skills. He liked gardening and used to spend a lot of his time gardening and reading books. Mendel had always wondered about inheritance and its pattern. He spent most of his time learning and exploring the pattern of inheritance. His principles are recognised worldwide as the laws of inheritance.

Mendel’s Life

Mendel was born by the name Johann Mendel in the village of Heinzen Dorf, Austria, in 1822 in a farmer’s family. Later he gained education in physics, mathematics and the basics of plant anatomy. He completed his education under personalities like Doppler (known for the Doppler effect) and Friedrich Franz (A well-known personality in applied physics and mathematics). Later he joined an Augustinian monastery and became known by Gregor Johan Mendel or G J Mendel. He also worked as a teacher of physics. Mendel got his interest in nature from his father. He did hybridisation experiments on pea plants. He did his significant scientific works and published his paper in 1862. Today’s famous Mendel went unnoticed at the time of his publication. Much after his death, his work was rediscovered, and he was given the due credit. He is referred to as the “father of genetics” because of his contribution to the field of genetics.

No Acknowledgement of Mendel’s Discoveries

Mendel’s work expanded genetic inheritance before DNA had even been discovered, yet most scientists did not accept his work when he was alive. Three main reasons for the non-acceptance of his works are listed below:

1. When he presented his research to other scientists, he did not convey it well, and they did not fully comprehend it.

2. It was published in a lesser-known scientific publication, so few people read it.

3. He was unable to explain the science behind why certain traits are inherited.

Rediscovery of Mendel’s Work

Three European botanists, Hugo DeVries, Carl Correns, and Erich von Tschermak, independently rediscovered Mendel’s work in the same year. It was almost a generation after Mendel’s discoveries were published. They created awareness about Mendelian inheritance laws among the scientific community and ensured Mendel’s due credit.

Mendel’s Experiment

Mendel had knowledge of mathematics, plant sciences and gardening. His monastery had lots of lands available for agriculture. He used artificial hybridisation techniques to cross plant and statistical tools like Punnett square to keep a tab of all his experimental data.

Mendel conducted his hybridisation experiments on garden pea between 1856 to 1863. He chose 14 plants of true breed. True breeds are those that have gone through continuous self-pollination. This causes stable trait inheritance. He performed emasculation (removal of anther) and bagging (covering stigma with butter paper) of flowers for his cross-pollination experiments, which prevented unwanted self-pollination.

General Terms Associated With Inheritance Study

Homozygous: A homozygous individual has identical alleles of a gene or factors of a character. Example- The true-breeding tall (TT) and true breeding dwarf plants (tt) are homozygotes.

Heterozygous: A heterozygous individual has nonidentical alleles of a gene or factors of a character. Example: A heterozygous pea plant has Tt alleles for height.

Genotype: It is the genetic makeup of an individual. Example: The genotype of a heterozygous pea plant for height is Tt.

Phenotype: It is an observational characteristic. Example: Phenotype of homozygous recessive ‘tt’ plant for height is dwarf whereas phenotype of homozygous ‘TT’, as well as heterozygous ‘Tt’, is tall.

Punnett Square: Punnett square is a tool used to visualise all potential allelic combinations of gametes in a cross of parents with known genotypes to predict the likelihood of their offspring having certain allele combinations.

Filial Generation: A generation in a breeding experiment that follows a mating between parents of two significantly different genotypes but usually relatively pure. The first generation obtained after mating between parents is called the first filial (F₁) generation, the second generation is called the (F₂) generation and so on.

Back Cross:  Cross between F₁ generation and either of the parents. When F₁ is crossed with a dominant parent, it is referred to as dominant back cross, and when it is crossed with a recessive parent, it is referred to as recessive back cross.

Test Cross: It is a particular case of the back cross where the F₁ generation is only crossed with a recessive parent. It is called test cross because this cross helps us identify the genotype of F₁ progeny. If both tall and dwarf progeny are obtained in a 1:1 ratio, it shows that the genotype of F₁ is heterozygous.

Reciprocal Cross: In the reciprocal cross, the sex of parents are reverted for a particular trait. If a tall parent was male in an experiment and the dwarf was female, then, the reciprocal cross tall female and the dwarf male plant are picked.

Monohybrid Cross: Inheritance of One Gene

In this experiment, Mendel crossed two pea plants with contrasting traits viz; height: one tall (TT) and one dwarf(tt). The first filial (F₁) generationprogeny was all tall(Tt). Then he crossed F1 progeny (Tt x Tt) and obtained second filial (F₂) generation with both tall and dwarf progeny in a 3:1 phenotypic ratio. 

He repeated the same experiment with different traits of Pisum sativum and obtained a similar result. The experiments gave phenotype information, so Mendel performed a test cross where he allowed crossing between F₂ and dwarf parent to understand genotype. He obtained tall and dwarf plants in a 1:1 ratio. Based on his observation, he gave the principle of dominance and segregation, which are known today as the law of dominance and segregation.

Dihybrid Cross: Inheritance of Two Genes

Mendel considered two traits for his dihybrid cross experiment viz; seed shape (round and wrinkled) and seed colour (yellow and green). Seed with round shape and yellow colour were dominant overseed with green colour and wrinkled shape. The F₁ generation was found to beround and yellow, whereas in the F₂ generation following phenotypic ratio was observed:

Round, yellow: wrinkled, yellow: round, green: wrinkled, green: 9:3:3:1.

Mendel’s Law

Law of Dominance

Alternative forms of the gene are called allele or allelomorphs. There are two variables, one dominant, which always expresses itself, and the other recessive allele, which expresses only in homozygous conditions.

Law of Segregation

The pair of alleles segregate randomly in gametes, i.e., each gamete receives only one allele of a gene.  Since gametes are haploid and contain only one allele for a character, they are considered pure; hence, this law is also called the law of purity of gametes.

Law of Independent Assortment

This lawstates that the alleles of two (or more)  genes get sorted into gametes independently of one another. In other words, the inheritance of one gene is independent of another gene.

Reason Behind Mendel’s Success

Mendel was not the first to carry out hybridisation experiments, yet he was the one who touched down. The reasons behind ar enlisted below:

1. He chose one character at a time. 
2. He carried out the hybridisation experiments for 2-3 generations to understand the pattern of inheritance.
3. He used statistical tools like Punnett square for data analysis and kept data records.
4. He carried out a test cross and back cross to analyse the pure line.
5. He chose a large sample size for his experiment.
6. The choice of his plant was pea ‘Pisum sativum’, which provided many advantages.

Practical Applications of Mendel’s Law

The following are some of the applications of Mendel’s laws:

1. We can determine new combinations in hybrid progeny and anticipate their frequency using Mendel’s principles.
2. Plant and animal breeders use this information extensively to create superior breeds.
3. Hybridisation can create new types of plants with new combinations of valuable characteristics.

Summary

Mendel was born by the name Johan Mendel in the village of Heinzen Dorf, Austria, in 1822 in a farmer’s family. He is referred to as the “father of genetics” because of his contribution to the field of genetics. Mendel had knowledge of mathematics, plant sciences and gardening. He chose garden pea or Pisum sativum plant for his experimental works after careful consideration. He chose seven pairs of contrasting characters found in pea plants. The traits he selected were: seed shape, flower colour, seed coat tint, pod shape, unripe pod colour, flower position, and plant height.  Mendel conducted his hybridisation experiments on garden pea. For the monohybrid cross, he considered only one pair of contrasting traits. For the dihybrid cross, he chose two pairs of contrasting traits. His principles proposed are known as laws of inheritance today. Mendel’s work was not accepted by most scientists when he was alive. Three European botanists, Hugo DeVries, Carl Correns, and Erich von Tschermak, independently rediscovered Mendel’s work and ensured Mendel’s due credit.

Frequently Asked Questions (FAQs)

Q.1. What are the three laws of inheritance?
Ans: Three inheritance laws are: Law of dominance, Law of segregation, and Law of independent assortment.

Q.2. Who is known as the father of genetics?
Ans: Mendel is known as the father of genetics.

Q.3. Who was Mendel, and what did he do?
Ans: Mendel was a monk by profession with a keen interest in science. He discovered the basic principle of inheritance.

Q.4. Which is the universal law of genetics?
Ans: Law of segregation is considered a universal law of inheritance.

Q.5. Why did Mendel perform his experiments?
Ans: Mendel did his experiments to determine how traits are passed down from one generation to another.

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