Question

In the Mexican Hairless breed of dog, the hairless condition is produced by the heterozygous genotype (Hh). Normal dogs are homozygous recessive (hh). Puppies homozygous for the H allele are usually born dead. If the average litter size at weaning (after nursing) is six puppies in matings between hairless dogs, what would be the average expected number (not a ratio) of hairless and normal offspring at weaning from matings between hairless and normal dogs?

A) 6 normal dogs and 2 hairless dogs

B) 2 normal dogs and 1 hairless dog

C) 5 normal dogs and 1 hairless dog

D) 3 normal dogs and 3 hairless dogs

E) 4 normal dogs and 4 hairless dogs

The answer is E, Can you tell me why is E? Thank you

Answer 1

Hairless dog genotype: Hh

Normal dog phenotype: hh

Lethal phenotype : HH

Mating between two hairless dongs :

Parents: Hh x Hh

Puppies: HH(Lethal), Hh, Hh hh

Why E.Lets see the mating between hairless and normal dog

Parents: Hh x hh

Puppies: Hh (hairless), Hh (hairless), hh (normal), hh (normal)

So there is no possibility for HH lethal genotype in above mating so there no death of any puppy, that's why four normal and 4 hairless puppies are possible