1. Tay-Sachs is a metabolic disorder that results in deterioration of the brain and nervous system, causing an early death in children (usually by age 5). The disease is caused by a recessive allele, ‘t’. Stuart and Lauren’s first child had Tay-Sachs disease.
Lauren is pregnant again.
State the genotypes of both parents and their first child.
What are the chances of their second child having the disease? Show your work.
Stuart:
Lauren:
First Child:
Probability of 2nd Tay-Sachs child:

2. Flat feet are inherited through a recessive allele, ‘f’
Flat feet are inherited through a recessive allele, ‘f’. Two people who have normal arches produced a child with flat feet.
What are the genotypes of all the family members?
What is the probability of their next child having flat feet?
Dad:
Mom:
First Child:
Probability of 2nd Flat-Foot child:

3. Just for fun – you think you know, but you don’t.
A couple has two children – one is a girl. What are the chances the other is also a girl?
Boy
Girl
25%
1 out of 3 – 33%