Question

A person heterozygous for the recessive gene for blue eyes marries a person who is homozygous for the trait. What is the probability that the couple's third child will have blue eyes?

Answer 1

There is a 50% chance that the couple's third child will have blue eyes, as one parent is heterozygous (Bb) and the other is homozygous recessive (bb) for the blue eye trait.

Step-by-step explanation:

The question is asking about the probability that a couple's third child will have blue eyes when one parent is heterozygous for the blue eye allele (Bb) and the other is homozygous recessive for blue eyes (bb). This is a classic example of a Punnett square problem in genetics.

In this case, the cross can be represented as:
Bb (heterozygous blue eyes) x bb (homozygous blue eyes).
The Punnett square would then look like this:

• Bb (heterozygous, not blue eyes)
• bb (homozygous recessive, blue eyes)
• Bb (heterozygous, not blue eyes)
• bb (homozygous recessive, blue eyes)

From this Punnett square, we can tell that there is a 50% chance for each child to be homozygous recessive (bb) for blue eyes and thus have blue eyes. Since the probability remains the same for each child the couple might have, the probability that their third child will have blue eyes is still 50%.