10th Class Science Heredity and Evolution Mendels Law of Inheritance

         Mendel’s Law of Inheritance

The laws of inheritance of traits in human being are related to the facts that both the parents contribute equally to the child development. The traits of the child can be influenced by DNA both the parents and thus for each traits there are two versions in each child. On the basis of this Mendel's worked out the main rules of inheritance, known as Mendel's laws of inheritance. Gregog J Mendel was a botanist from Australia, who is known as the father of genetics. Mendel performed an experiment with the pea plant to study the variation pattern of inheritance of different characters. He choose pea plant because it is self pollinating, easy to cultivate and have distinct defined character. In his experiment, he crossed a variety of pea plant of different traits, such as tall and dwarf plants, round and wrinkled seeds, white and pink flowers etc. These two plants are called parental generation and the generation that was produced by crossing these two plants was called the first generation (F₁). When the plants of F generation were crossed among themselves followed the generation called second generation (F₂).

Mendel gave the following conclusion from his experiment:

• The F generation plant shows only one of the traits which are crossed over and the other trait never appeared.
• The trait that did not appears in \[{{F}_{1}}\] generation reappeared in \[{{F}_{1}}\] generation, but it is only one fourth of the total number.

He called the traits, which shows it appearance in any generation as

When the traits of \[{{F}_{1}}\] were crossed among themselves, the 75% of plants in \[{{F}_{2}}\] generation were tall and 25% of them were dwarf. Thus, the phenotype ratio was 3:1.

After performing the experiments on the inheritance of traits of one character he performed an experiment with the two character or dihybrid cross. He crossed the plants of round and yellow seeds with the plants of wrinkled and green seeds: and found that all the plants \[{{F}_{1}}\] generation are round and yellow. When the plants of \[{{F}_{1}}\] generation were crossed among themselves he found that it gave rise to four types of seeds. Of these 301 were round and yellow, 102 were round and green, 96 were wrinkled and yellow and 30 were wrinkled and green. Hence their phenotype ratio was about 9:3:3:1.

The genotypic ratio of the dihybrid cross is found to be 1:2:2:4:1:2:1:2:1. He found that it was actually the gene which were responsible for the traits of an organisms. These traits are presents on the chromosomes of the genes of an organisms. It is the dominant gene which shows it character in the physical appearance of an organisms.