The colour of wheat seeds is controlled by two genes. The alleles (R₁ and r₁) of one gene assort independently to the alleles (R₂ and r₂) of the other gene. R₁ and R₂ produce a red pigment while r₁ and r₂ do not produce any pigment. The effect of the alleles is additive so that R₁/R₁; R₂/R₂ give dark red colour while r₁/r₁; r₂/r₂ produces white. A plant with R₁/r₁; R₂/r₂ has intermediate red colour. A plant heterozygous at both gene loci was allowed to self-fertilise. What proportion of offspring would be expected to have a colour similar to the parent? A) 0 B) 1/4 C) 3/4 D) 3/8 E) 1/2

Question

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The parent plant is heterozygous at both gene loci, so it will produce four types of gametes in equal proportions: R₁R₂, R₁r₂, r₁R₂, and r₁r₂. When these gametes self-fertilise, the offspring will have the following genotypes:1/16 R₁R₁; R₂R₂ (dark red)2/16 R₁R₁; R₂r₂ (intermediate red)2/16 R₁r₁; R₂R₂ (intermediate red)4/16 R₁r₁; R₂r₂ (intermediate red)1/16 r₁r₁; R₂R₂ (white)2/16 r₁r₁; R₂r₂ (white)1/16 r₁r₁; r₂r₂ (white)Therefore, 3/4 of the offspring will have a colour similar to the parent.

The Colour of Wheat Seeds Is Controlled by Two Genes