Changes in crossover distribution along a quadrivalent in a man carrier of a reciprocal translocation t(11;14)

A testicular biopsy from an infertile man carrying a heterozygous chromosome translocation t(11;14) was studied with synaptonemal complex analysis and immunolocalization of the protein MLH1 for crossover detection. A full blockage of spermatogenesis at the spermatocyte stage was related to the presence of the translocation quadrivalents at pachytene. Only 2% of the quadrivalents showed full synapsis. Most of the spermatocytes showed asynaptic free ends that frequently mingled with the XY pair. The average number of crossovers per cell was diminished from a mean of 52.7 in controls to a mean of 48 in the patient. The difference between the number of crossovers in the quadrivalent and the normal bivalents was highly significant. The distribution of crossovers over the segment of the quadrivalent corresponding to bivalent #14 was also very different from that of the control. It is concluded that in this translocation, the pattern of crossovers is changed, mainly due to a synaptic hindrance in the quadrivalent, and that the spermatogenesis arrest is mainly due to the quadrivalents that interact with the XY pair.