Question

What shall be the ratio in offspring, when a roan cow is crossed with a white bull?
A. 1:2:1
B. 3:1
C. 1:1
D. All roan

Answer 1

Let us first look into the meaning of what a codominance and incomplete dominance is. Incomplete dominance is a cross between the organisms with two different phenotypes producing offspring with a new phenotype that is blending with the both parental traits. Codominance is the form of inheritance in which both alleles of a gene pair are expressed.

Complete answer:
The cross between a roan bull (Ww) and red cow (WW) produces roan and red phenotypes in 1:1 ratio. A cross between roan bull (Ww) and white cow (ww) produces roan and white phenotypes in 1:1 ratio.
The examples of animals that show traits of codominance include speckled chickens, which contains alleles for both black and white feathers, and roan cattle, which allows to express alleles for both red hair and white hair. The codominance is also seen in plants.

Therefore the answer to the above question is option (C)- 1:1

Note: The best example of codominance is ABO blood group. The ABO blood grouping is completely controlled by the gene I which contains three alleles A, B, and O and will show codominance. The O allele is present as recessive to both A and B.
The codominant alleles that are present are the allele A and B and when both of them are present in a person they have the blood type of AB.
It does not matter if the alleles in the homologous chromosomes are dominant or recessive in codominance.
The homologous chromosome present consists of two types of alleles which produce proteins, and then both will be produced and forms a different phenotype or characteristics compared to that of the homozygote
Therefore, the trait present is neither recessive nor dominant.