Name: _______________________________________________________ Hour: _____ Number: _____

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Dihybrid Crosses Worksheet

For each of the following questions: A) Indicate the genotypes in the cross being made, B) Give all the

possible gametes for each parent, C) Show the Punnett square and D) Answer all the questions being

asked. Express probabilities as ratios.

1. In horses, black coat is dominate over chestnut. Also, trotting gait is dominate over pacing gait. A

horse who is homozygous for black coat color and trotting gait is mated with a horse with a chestnut

coat color and pacing gait. For possible offspring: A) List all possible genotypes and their

probabilities. B) List all possible phenotypes and their probabilities (as a ratio).

Cross: ________ X ________ Gametes: ____ ____ ____ ____ ____ ____ ____ ____

2. A homozygous black horse with a pacing gait is mated with a chestnut horse with a pacing gait. For

possible offspring: A) List all possible genotypes and their probabilities. B) List all possible

phenotypes and their probabilities.

Cross: ________ X ________ Gametes: ____ ____ ____ ____ ____ ____ ____ ____

Genotype probabilities:

Phenotype probabilities:

Genotype probabilities:

Phenotype probabilities:

Name: _______________________________________________________ Hour: _____ Number: _____

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3. In humans, right-handedness is dominate over left-handedness and normal skin pigment is

dominate over albinism. If a left-handed woman who is heterozygous for normal skin pigmentation

has a child with a man who is homozygous right-handed and albino, what is the probability that the

child will be a right-handed albino?

Cross: ________ X ________ Gametes: ____ ____ ____ ____ ____ ____ ____ ____

4. Sheila is right-handed and albino (and her mother is left-handed). Doug is left-handed and has

normal skin pigmentation, but both of his maternal grandparents are albino. What is the probability

of Shelia and Doug having a right-handed child with normal skin pigmentation?

Cross: ________ X ________ Gametes: ____ ____ ____ ____ ____ ____ ____ ____

Genotype probabilities:

Phenotype probabilities:

Genotype probabilities:

Phenotype probabilities: