The allele for brown fur in cats is recessive to the dominant allele for black f

Question

The allele for brown fur in cats is recessive to the dominant allele for black fur. Show work or/and reasoning. Is it possible for 2 black cats to have a brown kitten? Is it possible for 2 brown cats to have a black kitten? Polydactyly (more than 5 fingers on a hand) in humans is determined by a dominant allele. A normal woman is pregnant. Her husband has polydactyly but his mother did not. The woman is concerned that her child will be born with extra fingers and toes, especially since the child they already have has the condition. What is the chance that the next child will exhibit polydactyly? Show your work for full credit.

Explanation / Answer

6) Allele for brown fur is recessive (b)

Allele for black fur is (B)

Since black fur is a dominant trait expresses in both homozygous (BB) and heterozygous (Bb) states. Brown color express itself only in homozygous (bb) state.

A) When two black cats with genotype Bb mate, there is 1/4 th probability of getting brown kitten as shown in the following Punnett square.

B) Brown cats always have homozygous bb allele. So, they cannot produce black kitten.

7) Polydactyly is determined by dominant allele P. A normal woman with phenotype pp mates with man with polydactyly (PP or Pp)

Cross between PP and pp is shown below.

All the offsprings are affected if the husband's genotype is homozygous for polydactyly (PP). The second child has 100% chance of getting affected by polydactyly.

Cross between Pp and pp.

If the husband's genotype is heterozygous (Pp), half of the offsprings are affected and half are normal. The first child is already affected. So, the second child had 1/3 chance or 33.3% probability of being affected.

B b B BB Bb b Bb bb

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