Name: _________________________________________________________ Date: ______________ Period: ______
Autosomal Recessive Inheritance
Phenylketonuria (PKU) is a recessive condition where sufferers lack an enzyme to break down tyrosine in
their diet. Because it is recessive, both parents must pass down the gene in order for a child to inherit the
disorder. PKU, if left untreated, causes brain damage and retardation.
Both Angelica and George are healthy, but they are heterozygous (carriers) for the PKU disorder. This
means they each contain one healthy gene (H) but also one recessive gene (h). Angelica and George have
two children, Emma (age 12) and Gerald (age 7). Sadly, Gerald has been diagnosed with PKU, but Emma
has not.
Example: In the space below, complete a Punnett square in the space below.
Step 1: Set up the Punnett square below Step 2: Fill in the Punnett square below
1. According to the Punnett Square, what were the chances that Emma would be heterozygous/carrier?
2. According to the Punnett Square, what were the chances that Gerald would inherit PKU?
3. According to the Punnett Square, what were the chances that Angelica and George would have a
child that was homozygous dominant?
Example: Create a Pedigree in the space below that outlines all four people.
4. According to the Pedigree, which symbols show women?
5. According to the Pedigree, which symbols show men?
6. According to the Pedigree, how are individuals who suffer from the
disorder marked?
7. According to the Pedigree, what is another word for people who
are carriers of the disorder?
