Although a previous study of sperm recombinants indicated that recombination events at the DNA3 hotspot invariably resulted in fully reciprocal crossovers [20], it is not clear if this will also be true of female recombination, or whether the unusual distribution of PRDM9 genotypes among the parents of children with ALL [35] may influence the nature of crossovers at DNA3. This evidence concerns the gene PRDM9 and acute lymphoblastic leukemia.