Two genes 'A' and 'B' are linked. In a dihybrid cross involving these two genes, the F heterozygote is corssed with homozygous recessive parental type (aa bb). What would be the ratio of offspring in the next generation?
a) 1:1:1:1
b) 9:3:3:1
c) 3:1
d) 1:1
Solution:
The correct option (d) i.e. 1:1.
The cross between AABB X aabb will form gametes AB and ab. The F1 cross will form the offspring AaBb. Now when we cross AaBb with recessive parent aabb. Then only two gamete will be formed by AaBb and that is AB, ab. Ideally four gamete should have been formed but since A and B genes are linked therefore they will always remain together during gamete formation and will not assort independently. F2 generation will form only two types of offspring therefore the ratio of offspring in the second generation will be 1:1.
The ratio in F2 cross is 1:1
The correct option (d) i.e. 1:1.
The cross between AABB X aabb will form gametes AB and ab. The F1 cross will form the offspring AaBb. Now when we cross AaBb with recessive parent aabb. Then only two gamete will be formed by AaBb and that is AB, ab. Ideally four gamete should have been formed but since A and B genes are linked therefore they will always remain together during gamete formation and will not assort independently. F2 generation will form only two types of offspring therefore the ratio of offspring in the second generation will be 1:1.
The ratio in F2 cross is 1:1