An extra finger in humans is rare but due to a dominant gene. When one parent is normal and the other parent has an extra finger but is heterozygous for the trait, what is the probability that the first child will be normal?
*
4 points
50%
25%
75%
0%
The parent with an extra finger is heterozygous for the trait, which means they have one copy of the dominant gene (E) for the extra finger and one copy of the recessive gene (e) for normal fingers. The normal parent is homozygous recessive (ee).
When the parents have children, there are four possible combinations of alleles that their offspring can inherit: EE, Ee, Ee, and ee.
The only combination that would result in a normal child is ee, where both copies of the gene are recessive for normal fingers. This combination occurs with a probability of 25%.
Therefore, the probability that the first child will be normal is 25%.