Question

Grain colour in wheat is determined by three pairs of polygenes. Following cross AABBCC (dark colour) $\times$ aabbcc (light colour), in F${}_2$ generation what proportion of the progeny is likely to resemble either parent?

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

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 express only a part of trait and the full trait is expressed only in presence of dominant alleles of all multiple genes, is called as polygenic inheritance. A cross between AABBCC and aabbcc produces AaBbCc F${}_1$ hybrid. 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%. This is because polygenic trait expresses the full trait (parental phenotype) in pure breeding genotypes only.