Question

Describe the dihybrid cross experiment performed by Mendal. Explain the law postulated by this experiment.

Answer 1

A dihybrid cross is a cross between F${}_1$ offspring of two individuals that differ in two traits of a particular interest. For example, Mendel took homozygous dominant Round and yellow seeds (RRYY) and crossed it with homozygous recessive wrinkled and green seeds (rryy), the progeny obtained in F${}_1$ generation were all round and yellow seed (RrYy). The offsprings were heterozygous for both R and Y gene. The F${}_1$ plant has four types of gametes, RY, Ry, rY, and ry. For genes on separate chromosomes, each allele pair shows independent assortment. Thus, by crossing F${}_1$, the phenotypic ratio was 9:3:3:1, where 9 is yellow and round seeds, 3 represents round and green seeds, 3 represents yellow and wrinkled seeds and 1 represents green and wrinkled seeds.

Thus, Mendel's law of independent assortment was proved. According to Mendel's law of independent assortment, during the inheritance of two or more characters, the assortment of individual traits takes place independently during gamete formation. Thus each allele of a pair segregates independently and each gamete formed contains one allele of that trait.