Chiasma distributions along bivalents 1 and 14 in female and male mice were studied. It was shown that the average chiasma number in both chromosomes show no sex difference. There are however, significant sex differences in chiasma distribution along 1 and 14 chromosomes. In males there are two terminal chiasma peaks in chromosome 1 and one subtelomeric peak of chiasmata in chromosome 14. In females chiasma distributions are more even. According to genetic data, females produce more recombinants between loci of chromosome 1 than males do. By means of a computer simulation it was demonstrated that the differences in the average recombination frequency result from differences in chiasma distribution.