Suppose that the gene that determines how many fingers a person has is coded such that having 5 fingers is dominant and having 6 fingers is recessive. If a person's mother has 5 fingers and his father has 6 fingers, what is the probability that he will be born with 6 fingers?
A) 0 %
B) 50 %
C) 100 %
D) the percent cannot be determined because we do not know if his mother is homozygous or heterozygous for this trait

Question

Quizplus · Accepted Answer

Normally, recessive traits are only expressed when a person has inherited two recessive genes. In this example, if the person's mother is heterozygous for the trait, then the person would have a 50% chance of being born with 6 fingers. In this case, the father would contribute the recessive gene and there would be a 50% chance that the mother would contribute the recessive gene. As a result, there would be an overall 50% chance that the person would inherit both recessive genes and be born with 6 fingers. However, if the mother is homozygous for the trait, she will contribute the dominant gene which, even when combined with the recessive gene from the father, would never result in the presentation of the recessive trait of having 6 fingers. Thus, determining a precise probability would require that we know whether the mother is heterozygous or homozygous for the trait.

Suppose That the Gene That Determines How Many Fingers a Person