Question

Roan cattle show codominance for the color of their hair. there are alleles for red hair and white hair. what would you expect a heteozygous roan bull to look like if the trait showed incomplete dominance instead?

Answer 1

The answer is pink.

In incomplete dominance, a heterozygous phenotype is intermediate between two homozygous phenotypes. For this phenomenon, the symbols for alleles are capital letters. For example, allele A is responsible for red color of a hair, allele B is responsible for white color of the hair. Red cattle have AA genotype, and white cattle have BB genotype. By crossing cattle with red hair (AA) and white hair (BB), due to incomplete variance, the offspring will be heterozygous cattle (AB) with neither red nor white hair, but pink hair. Pink is an intermediate color between red and white.

Answer 2

The heterozygous roan bull would have pink hair due to the blending of alleles as a result of incomplete dominance.

Further explanation:

When both the alleles of a gene for a particular trait are expressed in an individual, they are said to be codominant. This means that neither of the alleles is recessive. Both the alleles are dominant and therefore, the phenotypic traits are expressed for both. The dominant alleles are those which suppress the expression of recessive allele. Two dominant alleles can be expressed at the same time or can be co-dominant which results in the expression of phenotypic traits of both the alleles. Codominance can be seen in both animals and plants which contain pigmentation. For example, a plant having flower petals of different colors and a dog with white and black spots.

The best example of codominance is the blood type in humans. The alleles A and B when expressed individually result in the A and B blood group whereas, when both the alleles are expressed together due to their dominant nature result in the formation of AB blood type.  

In incomplete dominance, neither of the alleles is completely dominant on one another. Therefore, none of them is expressed completely. As a result, a third phenotype is observed, which is a combination of the phenotypic trait of both the alleles. For example, when the white and the red plant of snapdragon are crossed with each other, the resulting progeny are pink in color. This is due to the incomplete dominance of red color-producing allele on the allele responsible for white color.

Here, there are two alleles for white and red hair color in the roan cattle. When the alleles show codominance, the roan will have an expression of both red and white hair whereas, if the alleles have incomplete dominance, the hair will be pink in color which is the intermediate expression of both the alleles for hair color.

Answer details:

Grade: College Biology

Subject: Genetics

Chapter: Gene interaction

Keywords:

alleles, genes, codominance, incomplete dominance, dominant, recessive, blood type, color, hair color, snapdragon, blood group, dog.