A phenotypically normal prospective couple seeks genetic counseling because the man knows that he has a translocation of a portion of his chromosome 4 that has been exchanged with a portion of his chromosome 12. Although he is normal because 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?

50% of sperms will be abnormal with duplication and deletions. There are 25% chances of production of normal sperms without any translocation while the rest 25% sperms will have balanced translocation.

Explanation:

A person with balanced translocation forms four types of gametes. There is a 25% probability of the formation of normal sperm. Segregation of homologous chromosomes during meiosis I would give 25% of the sperms with balanced translocation of chromosomes 4 and 12. Rest 50% sperms will exhibit deletion and duplication for the segments of chromosomes 4 and 12.

Out of the 50% abnormal gametes, half of the gametes will have a deleted segment of chromosome 4 and the duplicated segment of chromosome 12. Likewise, the rest of these gametes will have a deleted segment of chromosome 12 and a duplicated segment of chromosome 4. Therefore, there are 50% chances of the production of abnormal sperms.