Chapter 10, Problem 19A

Solution

To predict:

The reason some females produced rat terrier puppies without hair and some produced hairy puppies.

Introduction:

A dominant trait is the one which expresses itself in heterozygous condition. Any trait which is genetically determined is either autosomal or sex- linked trait. A recessive trait is the one which expresses itself only in homozygous condition.

As the presence of hair is genetically determined trait and some females are producing rat terrier puppies without hairs and others are producing puppies with hairs. This is because the presence of hair might be a sex-linked dominant trait while absence of hair can be a sex-linked recessive trait.

This case can be explained by the following cross.

Let X be a chromosome responsible for absence of hairs while X^h denotes the chromosome responsible for presence of hair and is a dominant trait.

If the gametes of dog is X,Y or if X^h,Y, the possible crosses may be

Gametes	X	Xh
X	XX	XXh
Y	XY	XhY

Gametes	X	Xh
Xh	XhX	XhXh
Y	XY	XhY

In these cases, all individual containing either on or both X^hwill be hairy while others will be non- hairy.