High-density comparative BAC mapping in the black muntjac (Muntiacus crinifrons): molecular cytogenetic dissection of the origin of MCR 1p+4 in the X1X2Y1Y2Y3 sex chromosome system.

The black muntjac (Muntiacus crinifrons, 2n = 8[female symbol]/9[male symbol]) is a critically endangered mammalian species that is confined to a narrow region of southeastern China. Male black muntjacs have an astonishing X1X2Y1Y2Y3 sex chromosome system, unparalleled in eutherian mammals, involving approximately half of the entire genome. A high-resolution comparative map between the black muntjac (M. crinifrons) and the Chinese muntjac (M. reevesi, 2n = 46) has been constructed based on the chromosomal localization of 304 clones from a genomic BAC (bacterial artificial chromosome) library of the Indian muntjac (M. muntjak vaginalis, 2n = 6[female symbol]/7[male symbol]). In addition to validating the chromosomal homologies between M. reevesi and M. crinifrons defined previously by chromosome painting, the comparative BAC map demonstrates that all tandem fusions that have occurred in the karyotypic evolution of M. crinifrons are centromere-telomere fusions. The map also allows for a more detailed reconstruction of the chromosomal rearrangements leading to this unique and complex sex chromosome system. Furthermore, we have identified 46 BAC clones that could be used to study the molecular evolution of the unique sex chromosomes of the male black muntjacs.