A phenotypically normal prospective couple seeks genetic counseling because the man knows that he has a translocation of a portion of his chromosome 4, which has been exchanged with a portion of his chromosome 12. Although his translocation is balanced, he and his wife want to know the probability that his sperm will be abnormal. What is your prognosis regarding his sperm?
A) One-quarter will carry the two normal chromosomes, 4 and 12, one-quarter will have only the two translocation chromosomes and no normal chromosomes 4 and 12, and half will have one normal and one translocated chromosome.
B) All will carry the same translocation as the father.
C) None will carry the translocation.
D) Half will be normal, and the rest will have the father's translocation.

Question

Quizplus · Accepted Answer

The father's translocation involves a portion of chromosome 4 and a portion of chromosome 12. As a result, there are three possibilities for the offspring's chromosomes: normal chromosomes 4 and 12 (from the mother) and normal chromosomes 4 and 12 (from the father); translocated chromosomes 4 and 12 (from the father); or one normal chromosome 4 (from the mother or the father) and one translocated chromosome 4/12 (from the father). The probability of each of these three possibilities is equal, which means that one-quarter of the offspring will carry the two normal chromosomes, one-quarter will have only the two translocation chromosomes and no normal chromosomes 4 and 12, and half will have one normal and one translocated chromosome. Therefore, the prognosis regarding the father's sperm is that half will be normal, and the rest will have the father's translocation.

A Phenotypically Normal Prospective Couple Seeks Genetic Counseling Because the Man