Figure 1.

Genetic recombination diversity in the Barcelona chromosomal polymorphism zone. (a) Map showing the sampling distribution. Diploid numbers are shown for each locality (see the electronic supplementary material, table S1). Locations with standard and Rb individuals are indicated in red and black, respectively. (b) Example of immunolocalization of meiotic recombination events in mouse spermatocytes at pachynema from Rb5 (2n = 37). MLH1 foci are depicted in green, centromeres in blue and the synaptomenal complexes in red. Asterisks indicate trivalent structures. (c) Fluorescence in situ hybridization on a metaphase spread from Rb3 (2n = 38) with the chromosomes involved in the Rb fusion painted in green (chromosome 4) and red (chromosome 14). (d) Distribution of the mean numbers of MLH1 foci per cell observed in the specimens analysed (n = 34): lab_strain, standard mice from laboratory strain (n = 310 cells); standard, wild standard mice (n = 349 cells); Rb, 2n = 39–37, Rb mice with diploid numbers between 2n = 37–39 (n = 270 cells); and Rb, 2n = 32–28, Rb mice with diploid numbers between 2n = 28–32 (n = 333 cells). Asterisks indicate statistical significance (Mann–Whitney U-test or Kruskal–Wallis test; *p-value ≤ 0.05, **p-value ≤ 0.001). (e) Percentage of chromosomal arms showing 0, 1 or 2 MLH1 foci. Three groups are differentiated: Ac_St, all acrocentric chromosomes belonging to standard wild mice (n = 1197); Ac_Rb, all acrocentric chromosomes from Rb mice (n = 2211); and Met, all chromosomal arms involved in Rb fusions (n = 2056). Asterisk indicates statistical significance (Kruskal–Wallis test, **p-value ≤ 0.001).