Question

In a cross between red kernelled and white kernelled varieties of wheat showing polygenic inheritance the phenotypic ratio of $F_2$ generation will be

• A. $1:6:15:20:15:6:1$
• B. $1:4:6:4:1$
• C. $1:2:1$
• D. $2:1$

Answer 1

Answer: (B)

$1:4:6:4:1$

In a polygenic crosses, the proportion of dominant or recessive homozygous individuals in the second generation, with the parent genotype, is equal to 1/Total. However, if the formation of the trait is controlled a single gene, the proportion of homozygotes individuals = 1/4, if two polygenes, the proportion = 1/16 if the three polygenes, the proportion = 1/64.
Hence in this case, parental genotypes for crosses between the white and red will be - "aabbcc" for white, and "AABBcc" or "aaBBCC" or "AAbbCC" for a light-red. All first-generation offspring will be light-red wheat (for example "AaBbcc"). As a result of crossing first-generation hybrids, we obtain the inheritance of the traits in the phenotypic ratio of 1:4:6:4:1.