Mendel’s Law of independent Assortment

In the next crosses, Mendel studied two contrasting trait at a time. Such crosses are called dihybrid crosses. He performed experiments on two seed traits i.e. shape and colour. The trait of round seeds was dominant over wrinkled seeds. Similarly yellow seed colour was dominant over green. Mendel crossed a true-breeding plant that had round yellow seeds with a true-breeding plant having wrinkled green seeds. All seeds in F1 generation were round yellow.

When F1 seeds grew into plants, they were self-fertilized. This cross produced seeds with four phenotypes. There were 315 round yellow seeds, 108 round green seeds, 101 wrinkled yellow seeds and 32 wrinkled green seeds. The ratio of these phenotypes was 9:3:3:1.

Mendel explained that the two traits i.e. seed shape and seed colours are not tied with each other. The segregation of ‘R’ and ‘r’ alleles happens indepdently of the segregation of ‘Y’ and ‘y’ alleles.

From his second experiment, Mendel concluded that different traits are inherited independently of one another. This principle is known as law of independent assortment. It states as: “the alleles of a gene pair segregate independently from the alleles of other gene pairs”