Question

Individuals with fusion-type translocations of chromosomes 13 and 14 are common (about ~1/1000). People who are heterozygous carriers for this translocation have lower rates of fertility and higher rates of miscarriage and stillbirth than the general population. About half of children that are born also have the translocation. Prior to the advent of modern medicine, carriers of these translocations would be expected to have fewer surviving offspring than the average.

1. Would individuals homozygous for the 13-14 translocation have reduced fertility?

Answer 1

a. Robertsonian translocation between 13 and 14 chromosomes is a centric fusion between the two acrocentric chromosomes.

Homozygous with Robertsonian translocation in chromosome 13 and 14 are rarely reported. It has been shown that 99.7% sperm from Homozygous translocation male are normal, as compared to 79.9% sperm being normal in heterozygous carriers. Nullisomy, disomy and diploid for the sex chromosomes levels in homozygous people were similar to normal people. The morphology and motility of sperm was also not affected. Loss of the short arms of the acrocentric chromosomes does not cause any deleterious effects. Hence, these homozygous individuals have normal fertility. Heterozygous carriers may have mal-segregated translocation chromosome, which can result in infertility. Thus, if a homozygous person marries a normal person, chances of getting heterozygous carriers that are normal is high. Homozygosity normally does not have any effect on meiosis (hence no effect on fertility) while heterozygosity causes disturbances in meiotic segregation.