1. Biology 1B Section 11.2, Punnett Squares
Heredity
Biology 1B
Section 11.2, Punnett Squares

2. Section 11.2 Objectives
4. Use punnett squares to predict the probability of genetic crosses
5. Discuss the design, results and conclusions of Mendel’s dihybrid cross experiment.
6. Explain the principle Independent Assortment

3. Punnett Squares
A punnett square is a chart used to predict the probable results (offspring) from a genetic cross
The punnett square is based on the principle of segregation
Start with the parent genotypes
Separate the alleles with equal probability

4. Completing a Punnett Square
Let’s assume a cross between two heteozygous parents
Bb x Bb
Use the law of segregation to set up the punnett square
One parent on top, the other on the side
Separate the alleles with equal probability

5. Completing the Punnett Square
Create allele pairs in the answer box by carrying parent alleles down and across
The allele pairs will be the genotypes of the offspring

6. Completed Punnett Square
From the cross Bb x Bb
The genotypes of the offspring will be
¼ BB
½ Bb
¼ bb

7. Punnett Square Practice
Complete Punnett Squares for the following crosses:
BB x Bb
Bb x bb
bb x Bb
bb x bb
BB x bb