Abstract:
This paper describes a case which presents
an evident variation from the ‘‘standard’’ XX/XY sex
chromosomal constitution in a rodent, Acomys sp. This
species known to be found in three localities of East
Africa has only recently been separated from A. spinosissimus,
its closest relative. In our study, five
specimens of Acomys sp. and eight specimens of
A. spinosissimus were live-trapped in five localities.
Comparisons between the two taxa assed by G- banding
show a complete homology in the chromosomal shape
and banding pattern for 29 pairs of chromosomes corresponding
to the complete autosomal set of A. spinosissimus.
However, while all the A. spinosissimus
analysed have 2n = 60 and a XY-XX system, in Acomys
sp. males and females constitute mosaics for sex
chromosomes in the bone marrow cells. Females
(2n = 59, 60) have an excess (97%) of aneuploid cells
with one single giant X chromosome, and males
(2n = 60, 61) show X0/XY cells occurring in somatic
tissues and XY cells in the germinal lineage. In addition,
an odd heterochromatic submetacentric chromosome
was identified in all the cells examined in two
males and a female of Acomys sp. Since this chromosome
was not related to sex determination and it is not
present in all the analysed specimens, it can be
considered as a B chromosome. Finally, the in situ
fluorescence hybridisation (FISH) with telomeric
probes showed a very intense interstitial telomeric
signal (ITS) at the medial part on the long heterochromatic
arm of the X chromosome. This could be due
to recent chromosomal rearrangement.
