Question

In Holstein cattle the allele for black hair color (B) is dominant over the allele for red hair (b), and the allele for polled (P), or lacking horns, is dominant for the allele for having horns (p). What is the expected phenotypic ratio of the offspring of a BbPp x BbPp cross if these alleles sort independently?’

Answer 1

Answer: The expected phenotypic ratio is- 9:3:3:1 ( that represents 9 Black hair and polled horns: 3 black hair with horns: 3 red hair and polled horns: 1 red hair with horns).

Explanation-

According to the information given in the question, in Holstein cattle the allele for black hair color (B) is dominant over the allele for red hair (b) whereas the allele for polled (P), or lacking horns, is dominant for the allele for having horns (p). As we know that, dominant allele ( depicted by capital letter such as B and P here) masks the expression of recessive allele ( depicted by small letter such as b and p here).

When parents with genotypes- BbPp ( Black hair and polled horns) are cross bred and alleles separate independently, they will produce 4 different phenotypes in the ratio -  9 Black hair and polled horns: 3 black hair with horns: 3 red hair and polled horns: 1 red hair with horns.

The genotypes produced by each parent are- BP, Bp, bP, and bp

Refer punnett square.