A review on the cytogenetics of the tribe Oryzomyini (Rodentia: Cricetidae: Sigmodontinae), with the description of new karyotypes
Author
Moreira, Camila Do Nascimento
Author
Ventura, Karen
Author
Percequillo, Alexandre Reis
0000-0001-9490-5457
cmoreirabio@gmail.com
Author
Yonenaga-Yassuda, Yatiyo
text
Zootaxa
2020
2020-11-06
4876
1
1
111
journal article
7983
10.11646/zootaxa.4876.1.1
4ee8b608-7c73-4980-9e86-3e3719e91c7f
1175-5326
4423612
190EC586-E14B-4AEF-A5EF-3DA401656159
Holochilus chacarius
Karyotype: 2n = 48 and FN = 56. Autosomal complement: five metacentric pairs (four large and one small), and 18 acrocentric pairs medium to small decreasing in size. Sex chromosomes: X, a medium acrocentric; Y, a small acrocentric. C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes, with the exception of one large metacentric pair. The X chromosome presented pericentromeric heterochromatic blocks, the Y chromosome was almost entirely heterochromatic. G-banding was also performed (
Nachman & Myers 1989
, pp 6668,
Fig. 1A
). The karyotype of
H. chacarius
was highly variable, with diploid number ranging from 48 to 55, and fundamental number from 56 to 60. This variation occurs within and between populations from
Paraguay
and
Argentina
(
Table 4
,
Fig. 5
), and was resulted from multiple Robertsonian translocations (
Nachman & Myers 1989
;
Nachman 1992a
). Furthermore, two different
types
of supernumerary chromosome were reported: B1 was a small to large metacentric or submetacentric chromosome that contains only centromeric heterochromatin, and B2 was a small acrocentric chromosome that was largely heterochromatic. The authors reported a pericentromeric inversion of a single X chromosome in one female, terminal euchromatic addition to the short arm of the X chromosome in nine specimens, euchromatic addition adjacent to the pericentromeric region in one autosomal pair of two specimens, and one female with only one X chromosome (
Nachman & Myers 1989
;
Nachman 1992a
).
In the original report,
Nachman & Myers (1989)
, and latter
Nachman (1992a)
, considered the fundamental number as the number of all chromosome arms, including sex and B chromosomes. Here the fundamental number was given as the number of autosomal arms, excluding sex and supernumerary chromosomes. A karyotype with 2n = 48 and FN = 60, was reported by
Gardner & Patton (1976)
for a sample from
Paraguay
, however this specimen presented a submetacentric X chromosome, that accounts for the difference from the former karyotype.
Vidal
et al
. (1976)
reported a karyotype variation for genus
Holochilus
, 2n = 50–54 and FN = 56–60, for samples from
Argentina
that seems to belong to
H. chacarius
. We assumed this correlation, as this variability of diploid and fundamental number was described only for
H. chacarius
, and due to the proximity of collection localities.