When a red grain variety of wheat is crossed with another white grain variety a $F_1$ hybrid is produced. On selfing if this, an $F_2$- generation is produced. How many of these resemble phenotypically to their parents (let grain colour of wheat controlled by three gene pairs)?

The correct option is D 2/64
Grain color in wheat is a polygenic trait. A polygenic trait is 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. Therefore, depending on the genotype these genes exhibit multiple phenotypes. According to the question, the grain color in wheat is controlled by three gene pairs. A cross between red grain (AABBCC) and white grain (aabbcc) varieties produce $F_1$ generation with AaBbCc genotype. Selfing of $F_1$ hybrids produce $F_2$ generation. The fraction of the parental genotype AABBCC is 1/64 and that of aabbcc is 1/64. Thus, the total fraction of $F_2$ generation having the parental genotypes and therefore, the parental phenotypes is 2/64. Thus, the correct answer is option C.