Question
I. How could our baby be an albino?
iffany and Joe have just had a baby and are very surprised to learn that their baby is albino
with very pale skin and hair color. Tiffany's sister comes in to visit Tiffany and the new baby, and
Joe goes out to talk with his sister Vicky.
Did Tiffany have an affair?
Joe is very angry. He tells Vicky, "I think Tiffany had an affair with Frank! He's the only albino we
know. Obviously, Tiffany and I aren't albino, so Frank must be the father.
Luckily, Vicky is a biology teacher, so she explains how two parents with normal skin color could
have an albino baby. She draws a Punnett Square to illustrate her explanauon.
Drawa Punnett Square to show how two parents with normal skin color could have an albino
Oaby. Use a for the recessive allele that can result in very pale skin and hair color and A for tne
dominant allele that results in normal skin and hair color.
to feel guilty for getting so mad. He says "Geez, I feel like a jerk now. I should
at Tiffany would never cheat on me." Vicky responds, "That's okay. You were
Just forget about it."
Joo
will Tiffany and Joe's next baby be albino?
Two years later, Tiffany is pregnant again, and she and Joe are discussing whether their second
baby will be albino. Tiffany thinks the baby probably will be albino, but Joe remembers Vicky's
explanation, and he tells Tiffany, "No, our second baby can't be albino because only one out of
every four of our children should be albino. We already have one albino child, so our next three
children should not be albino."
2. Is Joe right? Explain why or why not.
Answer
1. The Punnett Square for two parents with normal skin color having an albino baby would look like this:
| | A | a |
|---|---|---|
| A | AA | Aa |
| a | Aa | aa |
Both Tiffany and Joe must be carriers of the recessive allele (a) for their baby to be albino. This means that they each have one dominant allele (A) and one recessive allele (a). When they have children, there is a 25% chance that both parents will pass on the recessive allele, resulting in an albino child.
2. Joe is partially correct. The chance of having an albino child is 25% for each pregnancy, regardless of whether they have already had an albino child. However, the chance of having three non-albino children in a row is not guaranteed. Each pregnancy is independent of the previous ones, so the chance of having a non-albino child is still 75% for each pregnancy.