SBI 3U Genetics Processes

Genetics Problem Set I: Monohybrid Crosses & Punnett Squares

1. A brown eyed man and a brown eyed woman decide to have children. If both are heterozygous, what possible genotypes and phenotypes might their offspring have? Draw a Punnett square to illustrate their results. (Brown is dominant)

2. A pea plant, which is homozygous for the dominant axial flower, is crossed with a pea plant with terminal flowers. Draw a Punnett square to illustrate the genotypic ratio of phenotypic ratio.

3. Use a Punnett square to find the phenotypes and genotypes resulting from each of the following monohybrid crosses of pea plants:

A) homozygous tall will heterozygous tall

B) heterozygous tall with homozygous dwarf

4. Suppose that a cross had been performed with a garden pea, between parents with round seed (RR) and a parent with wrinkled seeds (rr). What would be the genotypes and phenotypes in the F1 generation? If two F1 offspring were crossed to produce F2 generation, what would be the resulting genotypes and phenotypes?

5. The houseplant coleus has curves on the edge of its leaves. Deep curves (D) are dominant over shallow curves (d). Draw a Punnett square showing the possible offspring of a cross between a heterozygous plant with deep curved leaves and a plant with shallow curved leaves. What are the possible phenotypes of the offspring? (HINT: shallow curves are a homozygous condition only).

6. In tomato plants, long vines (L) are dominant over short vines (l). The incomplete Punnett square below shows a cross between two tomato plants. Complete it by filling in the alleles of both parents. Identify the phenotypes of both parents and the offspring.

LL / LL
Ll / Ll

7. A black rabbit is crossed with a white rabbit and one of the seven offspring is white. What is the genotype of the black rabbit parent?

8. Assume that straight hair (c) is recessive to curly hair (C). Two curly-haired parents have straight-haired child.

a) Give two possible genotypes for curly haired people.

b) What is the genotype of the child?

c) What are the genotypes of the parents?

d) Using letter symbols show two different crosses between curly hair and straight hair. Indicate the phenotypes of the offspring in both cases.