Cytogenetic comparison of the lesser mouse deer (Tragu- lus javanicus) and the greater mouse deer (T. napu)

Mouse deer is known as the smallest and one of the most primitive ruminants. The lesser and the greater mouse deer originated in three different parts of Malaysia were examined for cytogenetic study. The chromosome number of the mouse deer was 2n=32, consisted of 15 metacentric autosome pairs and X and Y sex chromosome pair. G-, R-band revealed polymorphisms of sex chromosomes among the mouse deer from different origins. X chromosome varied in length of short arm between the lesser and the greater mouse deer. Y chromosome showed polymorphisms not only between the lesser and the greater mouse deer, but also among the lesser mouse deer from different origins. The 18S-28S rRNA genes (18S-28S rDNA) were localized only in the X and Y chromosomes in both lesser and greater mouse deer by the Fluorescence in situ hybridization (FISH) method. The hybridization signals of 18S-28S rDNA showed polymorphisms not only in size, but also in their distribution patterns on the sex chromosomes. In addition to the general banding methods, the FISH analysis determined that the greater mouse deer from Tioman island would be remarkably different from the lesser mouse deer. The cytogenetic observations investigated in this study could be informative to characterize the lesser and the greater mouse deer. And it is also suggested that the chromosomal change would reflect that the relationship between the geographic distribution and speciation among the mouse deer.