Question

In humans, the ABO blood type is under the control of autosomal multiple alleles.
Color blindness is a recessive X-linked trait.
Mom is type A and is color-blind.
Dad is type B and has normal vision.
They have a daughter who is type O and has normal vision.
What is the probability that their next child will be a son who is type AB and is color-blind?

make the answer into a fraction

Answer 1

Since the daughter is type O we know that each parent has to have an O allele.
Mom also has both X chromosomes carrying the color-blind allele.
Dad has 1 normal X (and a Y).

So the parental genotypes are:

Mom: AO and \(\sf X^c X^c\)
Dad: BO and XY

The crosses are then

What is the probability that their next child will be a son who is type AB and is color-blind?

Probability of having a son =\(\dfrac{1}{2}\)

Probability of having a kid with AB = \(\dfrac{1}{4}\) (see first punnet square)

Probability of having a son who is color-blind =1 (see second punnett square)

(all boys will be colo-blind because the mom can only give the \(X^c\) allele.

P(son that is AB and color-blind)=\(\dfrac{1}{2}*\dfrac{1}{4}*1=\dfrac{1}{8}\)