Describe dihybrid cross with a suitable example.

A dihybrid cross is a genetic cross between two organisms that differ in two pairs of contrasting traits.

For example, in pea plants, consider seed shape and seed color. Round seeds (R) are dominant over wrinkled seeds (r), and yellow seeds (Y) are dominant over green seeds (y).

When a plant with round yellow seeds (RRYY) is crossed with a plant having wrinkled green seeds (rryy), the F1 generation consists of plants with genotype (RrYy), all showing round yellow seeds.

When these F1 plants are self-crossed (RrYy × RrYy), they produce four types of gametes: RY, Ry, rY, and ry. The combination of these gametes results in four different phenotypes in the F2 generation: round yellow, round green, wrinkled yellow, and wrinkled green.

The phenotypic ratio observed is 9:3:3:1, which supports the law of independent assortment.

Thus, a dihybrid cross helps in understanding how two traits are inherited simultaneously.