Genetics, Father of Genetics and Mendel's law of Heredity

What is genetics

Every organism has many such qualities, which are passed on from generation to generation from parents to their offspring. Such traits are called Hereditary Characters or Hereditary Characteristics. The transmission of basic characteristics of organisms from one generation to another is called heredity. Due to the transmission of parent properties, the properties of each organism are similar to those of its parents. These traits are transmitted from one generation to the next through the gametes of the parents. Therefore, the transmission of parental traits from parents to their offspring through gametes from generation to generation is called heredity.

Who is the father of genetics

The branch of biology under which heredity and variation is studied is called genetics. Gregor John Mendel laid the foundation of modern genetics with his scientific discoveries. That is why he is also called the Father of Genetics.

A Brief Introduction to Gregor John Mendel

Gregor John Mendel, born on July 22, 1822, was a German-speaking Austrian priest and scientist. He is called the father of genetics. He determined the laws of genetics by experimenting on pea grains. The importance of his works was not recognized until the twentieth century, a later rediscovery of those rules revealed their importance. Gregor John Mendel died on January 6, 1884, sixteen years after that, the world came to know what a great scientist he was. In 1900, three European scientists discovered a forgotten article that had been published 30 years earlier. They knew its importance and spread its news in the scientific world.

Mendel's law of heredity

Mendel chose seven pairs of properties of peas for his experiments, each of which had the ability to suppress another property during the experiment. He called the first dominant and the second ineffective. Mendel expressed these factors responsible for the inheritance of traits with a symbol. Of the pairs of qualities, he expressed the factor of dominant trait in capital letter and the factor of recessive trait in English letter. For example, "T" for tallness and 't' for dwarfism.

According to Mendel, every germ cell has two factors to express the same property. When these two factors are equal, then this condition is called homozygous and when they are opposite, then this condition is called heterozygous. For example – – homozygous Tt – heterozygous Mendel studied the inheritance of first one pair of opposite traits and then two pairs of opposite traits, which are called monohybrid crosses and dihybrid crosses respectively.

Monocentric cross

When two plants are crossed on the basis of a unit trait, it is called monohybrid cross. In a cross , Mendel selected two such subspecies of pea plants, one tall and the other dwarf in pairs of opposite traits, and when it was crossed, it was seen that the plants produced by seeds in the first generation were all tall . All these first generation plants are called F1 plants. He then self-pollinated the plants obtained from the F1 generation and found that the phenotypic ratio of tall and short plants found in the second generation F2 was 3 : 1. This type of ratio is also called a hybrid ratio. There were three tall plants, one pure tall (TT) and two mixed or hybrid tall (Tt). A dwarf plant that formed from the F2 generation was a pure dwarf. If we get the third generation i.e. F3 from a plant of F2, then we will see that pure tall plants (TT) always form tall plants. Similarly, pure dwarf plants (tt) always form dwarf plants, but if mixed tall plants (Tt × Tt) are crossed, then the phenotypic ratio of tall and dwarf plants like F1 generation will be 3 : 1.

• Three tall and one dwarf plants of the F₂ generation have one pure tall (TT), two mixed tall (Tt) and one pure dwarf (tt) in the ratio 1 : 2 : 1. When crossed with F3 pure tall, only pure tall plants are obtained. like-

TT × Tr → TT

• When crossed with F₃ pure fat, only pure fat plants are obtained. like-

tt × tt → tt

• But after crossing mixed tall (Tt) with mixed tall (rt), again tall and dwarf (short) plants are obtained in the ratio of 3 : 1. in this-
  
  TT – Always Homozygous tall Tt – Heterozygous tall tt – Always Homozygous dwarf Its ratio
• Phenotypic ratio - 3 :1 (3 tall and 1 dwarf)
• Genotypic ratio - 1 : 2 : 1 (1 pure tall, 2 mixed tall and 1 pure dwarf)

Dihybrid Cross

A dihybrid cross is a cross between two different genes that differ in two observed traits. According to Mendel's statement, there is a completely dominant-recessive trait relationship between alleles of these two alleles. In the example, the RRYY/rryy parent resulted in F1 offspring that are heterozygous for both R and Y (RrYy). In the name "dihybrid cross", "Di" indicates that it contains two traits (eg R and Y), "hybrid" means that each trait has two different alleles (eg. R and r, or Y and y), and "cross" means that there are two individuals (usually a mother and father) who are adding or "crossing" their genetic information. The dihybrid cross is easy to visualize using a Punnett square of 16 dimensions:

The laws of meiosis, as they apply to dihybrids, are codified in Mendel's first law and Mendel's second law, also known as the law of segregation and the law of independent classification, respectively. For genes on different chromosomes, each allele pair showed independent segregation. If the first filial generation (F1 generation) produces four identical offspring, then the second filial generation, which occurs by crossing the members of the first filial generation, shows a phenotypic (appearance) ratio of 9 : 3 : 3 : 1, where-

• 9 represents the ratio of individuals displaying both the major traits.

RRYY + 2 x RRYy + 2 x RrYY + 4 x RrYy

• The first 3 represent the individuals exhibiting the first dominant trait and the second recessive trait.

RRyy + 2 x Rryy

• The second 3 represent those who exhibit the first predominant symptom and the second major symptom-

rrYY + 2 x rrYy

• 1 represents concurrent, both exhibits recurrent symptoms-

rryy dihybrid cross/ dihybrid cross ratio = 9:3:3:1 genotypic ratio: RRYY 1: RRYy 2: RRyy 1: RrYY 2: RrYy 4: Rryy 2: rrYY 1: rrYy 2: rryy 1.

Mendel's law

On the basis of monohybrid cross and dihybrid cross, Mendel formulated some laws of heredity, which is known as Mendel's law of inheritance. In these rules, the first and second are based on the basis of uni-cross and the third rule is based on the basis of bi-cross.

1. Law of Dominance: Under this, Mendel made a cross keeping in mind the opposite traits of a pair, then the trait present in the first generation was dominant. For example, when a tall pea plant is crossed with a dwarf plant, only tall plants grow in the first generation. This made the long dominant (Dominance) and the dwarf ineffective (Recessive) as per the rules. This law is also known as "Mendel's first law".
2. Mendel's law of segregation: According to this law, the factors of a pair of factors (genes) are separated during the formation of gametes and only one of these factors reaches the gamete. Both the factors never go into the gamete together. This law is also called the law of purity of gametes. For example, when a tall pea plant is crossed with a dwarf plant, only tall plants grow in the F1 generation, but again when the flowers of the same generation are self-pollinated, then the F2 generation plants are of both types. Here the ratio of 3 : 1 is found between tall and dwarf plants.
3. Law of independent assortment: According to this law, different pairs of factors that are found in an organism are independent of each other and can mix freely to form new forms of organisms. This rule is also called Daiisankar's experiment.

The genetic experiments Mendel conducted with pea plants took him eight years (1856–1863) and published his results in 1865. During this time, Mendel grew over 10,000 pea plants, keeping track of the number and type of ancestors. Mendel's work and his law were not admired in his time. It was not until 1900, after the rediscovery of his laws, that his experimental results were understood.

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