Discuss Mendel's dihybrid cross with checker board.

Explanation

A dihybrid cross is a cross involving two pairs of contrasting characters. For example, when a cross is made between yellow round and wrinkled green seeds (both pureline homozygous), plants with only yellow round seeds are seen in `F_(2)`-generation but in `F_(1)`-generation, four types of combinations are observed.
Two of these combinations are similar to the parental combinations and others are new combinations. These are round green and wrinkled yellow.
The cross can be seen as shown in the figure

  Phenotypic ratio Round yellow : Round green : Wrinkled yellow : Wrinkled green : = 9 : 3 : 3: 1
Genotypic ratio 1 : 2:2:4:1:2:1:2:1