Genetics Worksheet (Page 4 of 8) in pdf

Genetics Worksheet Page 4

Section C: Dihybrid Crosses

1. In guinea pigs, short hair is dominant to long hair and black eyes are dominant to red eyes. A male

guinea pig that is homozygous dominant for both traits is crossed with a female who has long hair and

red eyes. Complete a punnett square and determine the genotypic and phenotypic ratios.

Parents: ______ x _______

Possible gametes: _____ _____ _____ _____ x _____ _____ _____ _____

Genotypes:

Phenotypes:

You will need a separate sheet of paper for these problems.

2. In fruit flies, the allele for normal size wings (H) is dominant over the allele for vestigial wings (h). The

allele for normal size eyes (E) is dominant over the allele for small eyes (e). The genes for wing size

and eye size are on different chromosomes. Predict the results of a cross between a heterozygous

individual for both traits and an individual who is homozygous recessive for both traits. Complete a

punnett square and determine the genotypic and phenotypic ratios.

3. In racing horses, black hair (B) is dominant to chestnut hair (b) and a trotting gait (G) is dominant to a

pacing gait (g). Cross two horses that are heterozygous for both traits. Complete a punnett square and

determine the genotypic and phenotypic ratios.

4. Starting with a P generation with the following genotypes (AABB x aabb). Based on classical

Mendelian inheritance, what is the expected phenotypic ration observed among the F2 generation?

a. 9:3:3:1

b.1:2:1

c. 3:1

d. 1:1

e. 1:1:1:1

5. If AaBb is crossed with aabb, what proportion of the offspring would be expected to be aabb?

a. 9/16

b. 2/16

c. 4/16

d. 1/16

6. If the offspring of a cross show a 9:3:3:1 ration, the parents of the cross have the genotypes __.

a. AaBb x AaBb

b. AaBb x aaBB

c. aaBb x aabb

d. aaBb x Aabb

Genetics Worksheet Page 4