Question

Grain colour of wheat is determined by three pairs of polygenes. What proportion of F${}_2$ progeny will resemble either parents following a cross of AABBCC (dark colour) with aabbcc (light colour)?

• A. One third
• B. Half
• C. Less than 5%
• D. None of the above

Answer 1

The correct option is C Less than 5%

A trait governed by more than one gene where dominant allele of each gene expresses only a part of trait and the full trait is expressed only in the presence of all dominant alleles of all multiple genes, is called as polygenic inheritance. A cross between AABBCC (dark wheat grain) and aabbcc (light wheat grain) produces AaBbCc; F${}_1$ hybrid. Since grain colour is determined by three pairs of polygene; the genotypes having the dominant allele of all genes will show the phenotype of pure-breeding parents; rest genotype will show intermediate phenotypes. The hybrid produce 2${}^3$ = 8 gametes and selfing of gametes from two hybrids produce total 64 genotypes with 1/64 AABBCC and 1/64 aabbcc (the parental types). Thus, total number of parental types in F${}_2$ generation= 2/64= 3.12, i.e., less than 5%. The correct option is C.