HSA 2006 Biology Item 38

The length of a dog's tail is an inherited trait. The allele for short tails is dominant (T) over the allele for long tails (t). A dog breeder mates two short-tailed dogs (parents). One parent is homozygous and the other is heterozygous for this trait. A litter of twelve puppies, all with short tails, is produced (first generation). The breeder mates one of the first generation dogs with a short-tailed dog from another litter. A litter of ten puppies is produced (second generation). The breeder is surprised when one of the second generation puppies has a long tail.

Describe the genetic make-up of the parents and puppies that produced this inheritance pattern. In your response, be sure to

• identify the genotype of the parents
• use a Punnett square to show the possible genotypes of the first generation puppies
• use a Punnett square to show the possible genotypes of the second generation puppies
• identify the genotypic and phenotypic ratios of the first and second generation puppies
• explain how a long-tailed dog can suddenly appear when all the other dog's were short-tailed

Write your answer in your Answer Book.