Data from: Study of regional differences in GC content values in chromosomes of the guppy and related fish species

Genetic and physical mapping of the guppy (P. reticulata) have shown that
recombination patterns differ greatly between males and females. Crossover
events occur evenly across the chromosomes in females, but in male meiosis
they are restricted to the tip furthest from the centromere of each
chromosome, creating very high recombination rates per megabase, similar
to the high rates in of pseudo-autosomal regions (PARs) of mammalian sex
chromosomes. We here used the intronic GC content to indirectly infer the
recombination patterns on guppy chromosomes. This is based on evidence
that recombination is associated with GC-biased gene conversion, so that
genome regions with high recombination rates should be detectable by high
GC content. We used intron sequences and 3rd positions of codons,
in order to make comparisons between sequences that are matched,
as far as possible, with respect to selective constraints. Both these
types of sites are likely to be under weak selection. Almost all guppy
chromosomes, including the sex chromosome (LG12), prove to have very high
GC values near their assembly ends, suggesting high recombination rates
due to strong crossover localisation in male meiosis. Our test does not
suggest that the guppy XY pair has stronger crossover localisation than
the autosomes, or than the homologous chromosome in a closely related
fish, the platyfish (Xiphophorus maculatus). We therefore conclude that
the guppy XY pair has not recently undergone an evolutionary change to a
different recombination pattern, or reduced its crossover rate, but that
the guppy evolved Y-linkage due to acquiring a male-determining factor
that also conferred the male crossover pattern. The results also identify
the centromere ends of guppy chromosomes, which were not determined in the
guppy genome assembly.