Dihybrid Inheritance (Two Visible Contrasting Characters): Mendel took pea plants having two different characteristics: of seeds such as round shape with yellow colour and wrinkled shape with green colour, and crossed them. He found that only round-yellow seeds were produced in the F₁ progeny. Then he used F₁ progeny to generate F₂ progeny by self-pollination. He got four different combinations of seeds: round – yellow, round – green, wrinkled – yellow and wrinkled-green in the ratio of 9 : 3 : 3 : 1. This ratio is known as dihybrid ratio.