Dihybrid Crosses

Dihybrid Crosses

1.  In watermelons, solid green (G) color is dominant over striped pattern (g), and short shape (S) is dominant over long shape (s). What is the genotype and phenotype of all the possible offspring if you cross a homozygous green, heterozygous short watermelon with a heterozygous green, long watermelon?

2.  Using the information from above, give the genotype and phenotype of the offspring for a striped homozygous short watermelon and a green, short watermelon that’s heterozygous for both traits.

3.  In guinea pigs, black coat color is dominant to white, and short hair length is dominant to long. Indicate the genotypes and phenotypes for the following crosses:

a)  Homozygous black, heterozygous short-haired guinea pig with white, long-haired guinea pig.

b)  Heterozygous black short-haired guinea pig with white, long-haired guinea pig.

c)  Homozygous for black and long hair guinea pig with heterozygous black and short-haired guinea pig.

d)  For each of these crosses, give the probability that an offspring will have:

i.  Black coat, long hair

ii. Black coat, short hair

iii.  White coat, long hair

4.  For guinea pigs, black hair is dominant to white hair. Short hair is dominant to long hair. A guinea pig that is homozygous for both white and short hair is mated to a guinea pig that is homozygous for both black and long hair. Indicate the phenotype(s) of the F1 generation. If two hybrids from the F1 generation are mated, determine the phenotypic ratio of the F2 generation.

5.  T = tall, t = short; B = brown hair, b = blonde hair

Cross a homozygous tall, heterozygous brown-haired male with a heterozygous tall, blonde-haired female. Use a Punnett square to show parents and gametes.

a)  What is the phenotypic ratio of the offspring?

b)  How many offspring are homozygous for both characteristics?

c)  How many offspring are heterozygous for both characteristics?

6.  Assume that curly hair is dominant to straight hair. Albinism is a condition in which cells that normally produce pigment do not do so. The allele for skin albinism is recessive to the normal allele. A woman with curly hair and albinism and a man with straight hair and normal pigmentation have a child that has straight hair and is an albino. What are the genotypes of the parents?

7.  In a particular dog, short hair is dominant over long, and dark is dominant over light. One dog is heterozygous for hair length and shows the recessive trait for hair color. Another dog is homozygous dominant for hair length and heterozygous for hair color. Identify the possible phenotypes of the offspring and give the number of each expected.

8.  A plant of genotype TTYy was crossed with one of genotype ttYy. If the cross yielded 800 seeds, what number of what phenotypes probably resulted? What were their genotypes?

9.  In Drosophila, the allele for short legs (d) is recessive to the allele for normal legs (D), and the allele for hairy body (h) is recessive to the allele for normal body (H). Make a Punnett square for each of the following crosses.

a)  DdHh x Ddhh

b)  DDHh x Ddhh

c)  DdHh x ddhh

d)  What proportion of the offspring from the cross in (b) would be expected to show the normal phenotype for both traits?