Question

3. In crosses between guinea pigs of a certain variety, offspring have either brown or yellow

hair, which is either long or short. Assume that the traits are each single gene traits. Consider

the following crosses and the resultant F1 progeny:

Cross 1

P: female with long, brown hair X male with long, brown hair

F1: long, brown

short, yellow

long, yellow

short, brown

Cross 2

P: female with long, brown hair X male with short, yellow hair

F1:

long, brown

short, yellow

long, yellow

short, brown

a. Based on the data, which of the traits is dominant?

b. Assign genotypes to the parents in each of the crosses.

c. If each of the pairs of parents were to produce 80 guinea pigs over their lifetime, how many

of each type would you expect?

Answer 1

a. Long is dominant over short and Brown is dominant over yellow

b. it is provided above

c.

in cross -1 (phenotype ration is 9:3:3:1)

long, brown = 45

short, yellow = 15

long, yellow = 15

short, brown = 5

In cross: 2

as you see all 25%

so

long, brown = 20

short, yellow = 20

long, yellow = 20

short, brown = 20