Question

Two genes ‘A’ and ‘B’ are linked. In a dihybrid cross involving these two genes, the F${}_1$ heterozygote is crossed with homozygous recessive parental type (aa bb). What would be the ratio of offspring in the next generation?

• A. 1 : 1 : 1: 1
  
• B. 3 : 1
  
• C. 9 : 3 : 3 : 1
  
• D. 1 : 1

Answer 1

The correct option is D 1 : 1

Dihybrid cross

A cross involving two pairs of contrasting characters is called a dihybrid cross. In the given question, two genes ‘A’ and ‘B’ are linked.

A dihybrid cross involving these two genes, (AABB x aabb) results in the formation of the F${}_1$ heterozygous individual AaBb.

Test cross :

A cross between a dominant phenotype (F${}_1$) with unknown genotype and a homozygous recessive parent is called a test cross. In the given question, the F${}_1$ heterozygous progeny (AaBb) is crossed with homozygous recessive parental type (aabb). So, it is a test cross. In this case, the genotypic ratio of F${}_2$ generation is 1:1 (AaBb:aabb = 1:1), because the genes are linked and located in the same chromosome and they remain together in the gametes. This is due to the inability of linked genes to segregate and assort independently.

Final answer :
d.) 1 : 1