A- and B-chromosome pairing and recombination in male meiosis of the silver fox (Vulpes vulpes L., 1758, Carnivora, Canidae).

We examined A- and B-chromosome pairing and recombination in 12 males from the farm-bred population of the silver fox (2n = 34 + 0-10 Bs) by means of electron and immunofluorescent microscopy. To detect recombination at A and B chromosomes, we used immunolocalisation of MLH1, a mismatch repair protein of mature recombination nodules, at synaptonemal complexes. The mean total number of MLH1 foci at A-autosomes was 29.6 foci per cell. The XY bivalent had one MLH1 focus at the pairing region. Total recombination length of the male fox genome map was estimated as 1,530 centimorgans. We detected single MLH1 foci at 61% of linear synaptic configurations involving B chromosomes. The distribution of the foci along B- and A-bivalents was the same. This may be considered as a first molecular evidence that meiotic recombination does occur in mammalian B chromosomes. There was no correlation between the number of synaptic configurations involving B chromosomes per cell and the recombination rate of the A-genome.