Question

In rabbits, short hair is due to a dominant allele, S, and long hair to its recessive allele, s. Black hair is due to a dominant allele, B, and white hair to its recessive allele, b. When two rabbits are crossed, they produce 2518 short-haired, black offspring and 817 long-haired, black offspring. What are the possible genotypes of the parents?

Answer 1

Answer:

SsBB x SsBB

or

SsBB x SsBb

Explanation:

SS- short hair

ss - long hair

BB- black hair

bb- white hair

Total the number of offspring produced = 2518+817=3335

Where 2518= short haired, black offspring SSBB or SsBb

817= Longed Hair, black offspring ssBB or ssBb

To get the offspring proportion for short hair black offspring

2518/3335×100 = 75.5%

long-haired, blackoffspring =817/3335×100 = 25%

This gives ratio of 3:1 as against the proposed dihybrid phenotypic ratio of Mendel experiment 9:3:3:1

Now, if you remember a dihybrid cross results in 9:3:3:1 phentoype ratio. That is when both parents are heterozygous for both alleles. So we can rule that out since it doesn't match our 3:1 ratio.

Since all the offspring are black , it means one parent is homozygous dominant for black and the other parent is either homozygous or heterozygous for the black allele.

Since the ratio is 3:1, for the hair length

That leaves us with the short hair. Since the ratio is 3:1, both parents are heterozygous for hair length.

Therefore, the possible parental genotype is

SsBB x SsBB

or

SsBB x SsBb