Punnett Squares

Genetics and Evolution Lab

Part 1: Examples

A Punnett square can be used to predict the genotypes of the offspring of two parents.

Example 1: Freckles are a dominant trait with the dominant allele written as F and the recessive allele as f. A child has parents who are both heterozygous for freckles (genotype Ff).

Draw a Punnett square
What are the possible genotypes of the child?
What are the possible phenotypes of the child?
What is the probability that future children will have freckles?

Example 2: A woman with blood type O has children with a man who has type B blood (heterozygous).

Draw a Punnett square
What are the possible genotypes of the children?
What are the possible phenotypes of the children?
What is the probability that future children will have each blood type?

Part 2: Problem Set

In your groups, answer the following questions using Punnett squares.

Question 1

Attached earlobes are a recessive trait and can be represented by the letter a. A woman with free earlobes (heterozygous) has children with a man who has attached earlobes. Create a Punnett square and answer the following questions about the genotypes and phenotypes of their children.

In what ratio will these genotypes appear (AA:Aa:aa)?
In what ratio will the phenotypes appear (attached earlobe:free earlobe)?
What is the probability these parents will have a child with attached earlobes?

Question 2

A man who is heterozygous for blood type A married a woman who has blood type AB. Create a Punnett square and answer the following questions about the genotypes and phenotypes of their children.

In what ratio will the offspring genotypes appear?
In what ratio will the offspring phenotype appear?
What is the probability these parents will have a child with Type B blood?

back to Genetics and Evolution Lab main page

Page updated

Report abuse