Question

Case: Purebred shorthorn cattle of white coat (WW) were crossed with purebred cattle of red coat (RR). The $F_1$ cattle had coats with patches of white and red side by side.
What is the phenomenon responsible for this feature?

• A. Co-dominance
• B. Multiple alleles
• C. Incomplete dominance
• D. Independent assortment

Answer 1

The correct option is A Co-dominance

Co-dominance is a phenomenon in which both the alleles of a gene are dominant and are expressed independently in a heterozygous condition. As a result, traits associated with each allele are displayed simultaneously. The red and white coat colour in shorthorn cattle are controlled by co-dominant alleles and due to this, their hybrid ($F_1$ generation) is of roan coat colour (RW) i.e., patches of white and red.

Incomplete dominance is when a dominant allele does not completely mask the effects of a recessive allele, and the organism's resulting physical appearance shows a blending of both alleles. The case given above does not show a blending of both alleles, rather both are expressed equally.

Multiple alleles refer to the occurrence of more than two alleles for a particular gene. The given case does not mention the presence of more than two alleles for coat colour in shorthorn cattle populations. Hence, this is not a case of multiple alleles.

Independent assortment is applicable for the inheritance of two genes. Since the given example discusses inheritance of one gene only it is not applicable for independent assortment.