DNA organization along pachytene chromosome axes and its relationship with crossover frequencies

MLH1- focus map along SC1
The construction of crossover frequency histograms from MLH1 foci in birds and other vertebrates is fully explained in several publications (Pigozzi and Solari 1999; Borodin et al 2008). Briefly, individual SC lengths, centromeric signals, and MLH1 foci were scored using version 3.3 of the MicroMeasure program [53] which records absolute and relative distances on digitized images. To generate the recombination maps of the SC1, we calculated the absolute position of each MLH1 focus by multiplying the relative position of each focus by the average absolute length of the chromosome arm. These data were pooled for each arm and graphed in histogram form. The genetic map length in cM of each interval in this histogram (bin size 0.25 µm) was calculated multiplying the average number of MLH1 foci by 50. To produce the cumulative cM distribution, the average number of MLH1 foci per interval was converted to cM and then added along the SC starting from the tip of the short arm.
Foci on microbivalentes 9-38. The number of foci is the average scored in 138 nuclei.