Genome-wide reduction in recombination of backcross progeny derived from male versus female gametes in an interspecific cross of tomato.

We have determined that meiotic recombination differs between male and female gametes derived from the same plant. A single F1 plant was backcrossed to each of the parents, Lycopersicon esculentum and L pennellii, as the male (BCE) and female (BCP) parent, respectively. A total of 85 RFLP markers, covering more than 75% of the tomato genome, was used to construct a genetic map for both populations. Since both recurrent parents were homozygous, recombination measured in each population reflects crossing-over rates leading to male (BCE) and female (BCP) gametes. Comparisons were made by interval (genetic distance between two adjacent markers), by chromosome, and for the total length of the genome. Significantly less recombination was observed for male gametes at all levels. No significant relationship was found between areas of reduced recombination and approximate location to the centromere. That selection plays some role could not be eliminated, but no clear evidence was observed for single-locus selection as a major factor in the general reduction of crossing-overs in male gametes.