When a female cow with black hair is crossed with a bull with white hair, the offspring are known as blue roans because of their dark blue-gray color. A close examination of a blue roan’s coat shows a mixture of white hairs and black hairs. This is caused by:

1) sex linked traits
2) codominance
3) incomplete dominance
4) polygenic trait

2) codominance

Explanation:

CODOMINANCE is a non-mendelian pattern of inheritance which occurs when the alleles of a particular gene is neither dominant nor recessive over its contrasting allele, hence, they are both expressed in the resulting hybrid when they combine. The two alleles are said to be CODOMINANT.

This is the case in this question involving a gene coding for hair color in cattle. The allele for black hair is codominant with the allele for white hair, hence, they combine to form an hybrid with both colors expressed (black and white) called blue roan.

According to the attached image, the heterozygous genotype in the offspring exhibits a phenotypic expression of both traits under CODOMINANCE inheritance pattern.

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