Question

Grain colour in wheat is determined by three pairs of polygenes. Following cross AABBCC (dark colour) x aabbcc (light colour), in $F_2$ generation what proportion of the progeny is likely to resemble either parent?

• A. None
• B. Less than 5 per cent
• C. One third
• D. Half

Answer 1

The correct option is B Less than 5 per cent

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 produces 2${}^3$ = 8 gametes and selfing of gametes from two hybrids produce a total of 64 genotypes with $\frac{1}{64}$ AABBCC and $\frac{1}{64}$ aabbcc (the parental types). Thus, total number of parental types in $F_2$ $generation=\frac{2}{64}X100=3.12$%, which is less than 5%.