Multipoint linkage map of the human pseudoautosomal region, based on single-sperm typing: do double crossovers occur during male meiosis?

Sperm typing was used to measure recombination fractions among pseudoautosomal markers and the beginning of the X/Y-specific sequences located at the pseudoautosomal boundary. These experiments included primer-extension preamplification and PCR followed by allele typing using gel electrophoresis. A newly developed data-analysis program allowed the construction of the first multipoint-linkage sperm-typing map, using results obtained on seven loci from three individuals. The large sample size not only confirmed the increased recombination activity of the pseudoautosomal region but allowed an estimate of interference of recombination to be made. The coefficient of coincidence was calculated to be .26 over a physical distance of only approximately 1,800 kb. The observation of a few sperm presumably resulting from double recombination argues that more than one crossover event can occur in this region during male meiosis.