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Biology · Ch 3 — Inheritance and Variation

Co-dominance

Co-dominance

b. Co-dominance :

In co-dominance, both alleles of a pair express themselves fully and simultaneously in the heterozygote, rather than blending as in incomplete dominance. The classic example given is coat colour in cattle: crossing a red-coated animal (RR) with a white-coated animal (WW) produces roan offspring (RW) whose coats show a genuine mixture of red hairs and white hairs side by side — both traits visibly present together, not merged into an intermediate colour. …

Figure 3.2Co-dominance in cattle coat colour: a red (RR) parent crossed with a white (WW) parent gives roan (RW) F1 calves carrying both red and white hairs; selfing the roan F1 gives an F2 of red RR, roan RW and white WW in the ratio 1:2:1, with genotypic and phenotypic ratios identical
Fig. 3.2 — Co-dominance in cattle coat colour: a red (RR) parent crossed with a white (WW) parent gives roan (RW) F1 calves carrying both red and white hairs; selfing the roan F1 gives an F2 of red RR, roan RW and white WW in the ratio 1:2:1, with genotypic and phenotypic ratios identical

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What this figure shows. Illustrates the classic roan-cattle example where a red-coated (RR) animal crossed with a white-coated (WW) animal produces RW offspring that show both parental hair colours side by side rather than blending, because both alleles are expressed fully and simultaneously; selfing the roan F1 recovers red, roan and white in a 1:2:1 ratio identical to th …

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