Question

In some breeds of cattle, coat colour is inherited through incomplete dominance. When two red-coated cattle breed to one another, only red-coated offspring result. When a red-coated cow mated to a white-coated bull, roan (a lighter red/pink colour) coloured offspring resulted. What result would you expect from breeding two roan coloured cattle?
(a) $50\%$ red-coated cattle, $50\%$ white-coated cattle
(b) $25\%$ red-coated cattle, $50\%$ white-coated cattle, $25\%$ roan coated cattle
(c) $50\%$ roan-coated cattle, $50\%$ white-coated cattle
(d) $50\%$ red-coated cattle, $50\%$ roan-coated cattle
(e) $25\%$ red-coated cattle, $50\%$ roan-coated cattle and $25\%$ white-coated cattle.

Answer 1

Hint: In incomplete dominance after the crossing, the dominant allele is not able to express itself over the recessive allele. In the case of homozygous allele crossing the result of offspring is the same as a parent but in the case of heterozygous allele cross, an intermediate type of offspring gets formed.

Complete answer:
In the given question the red-coated cow and white bull are pure breeds in which red-coated cows consist of (RR) homozygous dominant alleles whereas the white-coated bull consists of (rr) homozygous recessive alleles. When crossing takes place between both the alleles then an intermediate roan colour offspring gets formed with allele (Rr).
If the cross takes place between two roans coloured cattle then crossing between two heterozygous alleles take place like (Rr)×(Rr) which results in four offspring with allele RR, Rr, Rr and rr which show that one is dominant with red colour coat and one is recessive with white colour coat whereas two intermediate with the roan colour coat. So the expected result of cattle breeding is $25\%$ red-coated cattle, $50\%$ roan-coated cattle and $25\%$ white-coated cattle.

So, the correct answer is $25\%$ red-coated cattle, $50\%$ roan-coated cattle and $25\%$ white-coated cattle.

Note:
In incomplete dominance, the allele does not possess an independent effect and the hybrid results in a new phenotype that does not resemble parents. In this, the phenotypic effect of one allele is more than that of other alleles.