To the Editor: It has long been accepted that productive recombination between X and Y chromosomes in humans is limited to short telomeric portions known as pseudoautosomal regions. It now appears that our picture of X-Y chromosome recombination requires revision because of the observation that gene conversion between X and Y gametologous regions occurs in humans, as reported by Rosser et al.1 in the July 2009 issue of the American Journal of Human Genetics. The data were based on resequencing of X and Y copies of a translocation hotspot (HSA)2 adjacent to the PRKX (MIM 300083) and PRKY (MIM 400008) genes.