1. Punnett Squares

2. Sample Problem In peas, yellow is dominant to green.
A homozygous green pea plant is crossed with a heterozygous yellow pea plant.
What is the phenotype ratio of the next generation?

3. Punnett Square Use 1. Write a let statement!
Let capital letter = dominant trait
Lowercase letter = recessive
2. Determine the parent’s genotypes (letters).
3. Draw Punnett Square.
4. Fill in Punnett Square.
5. Answer question.

4. Sample Problem In peas, yellow is dominant to green.
A homozygous green pea plant is crossed with a heterozygous yellow pea plant.
What is the phenotype ratio of the offspring?
Solution:
Let Y = yellow, y = green
Homozygous green: yy
Heterozygous yellow: Yy

5. yy x Yy y y Y Y Y y y y y y y y Solution: Phenotype ratio:
2 yellow : 2 green y y Y Y Y y y y y y y y