L5-6 Task: Punnett Squares
Punnet squares are used to look at the probability of the offspring of two parents having a specific
characteristic based on the parents Genotype.
In the examples below we are looking at eye colour as an example of a trait. “B” represents the dominant
brown allele and “b” represents the recessive blue allele.
Draw each of the following punnet squares into your copy books and for each one label:
a.
b.
c.
d.
1.
2.
3.
If the father and mother are homozygous or heterozygous
If they are homozygous, are they homozygous dominant or homozygous recessive?
Complete the punnet square to show the possible genotypes of the offspring
Write the probability of having a child with blue eyes
4.
5.
L7-8 Task: Write the answers to the following questions in your copy books
1. Draw a punnet square to show the probability of a heterozygous mother and a
homozygous dominant father having a child with blond hair. Use B for brown hair
(dominant over blond) a b for blond hair (recessive). Write the probability of a brown
haired child and probability of a blond haired child.
2. If a heterozygous man with dimples fathers a child with a woman with no dimples what is
the probability of a child with dimples? Use the following: Dimples (D) and no-dimples (d).
3. Exam question: What determines the colour of your eyes? Key words to include:
inheritance, chromosomes, genes, alleles, dominant, recessive