Chromosome numbers of marsupials vary between 2n = 11 B 10 @ and
2n =24. Most species have 14 or 22 chromosomes. There is no evidence that
polyploidy has occurred in marsupial evolution.
The Dasyuridae have 12 metacentric autosomes, a small metacentric
X-chromosome and a very small Y-chromosome (20% of living species have
been studied) and the chromosomes of Myrmecobius fasciatus are typically like
those of other Dasyuridae.
The Peramelidae (30% of species have been studied) have chromosomes
like the Dasyuridae except that X- and Y-chromosomes are much larger. The
occurrence of similar chromosome numbers in Dasyuridae and Peramelidae is
not necessarily evidence of affinity.
The chromosomes of the Phascolomidae are similar in number and
morphology to those of the Peramelidae and the resemblances are, almost
certainly, due to parallel evolution. The chromosomes of Phascolarctos are
unlike those of any of the Phalangeridae and this genus might be just as easily
grouped with the Phascolomidae.
The Phalangeridae have considerable chromosomal heterogeneity but less
than 20% of species have been studied. Two species of Cercaertus have 12
metacentric autosomes and small sex chromosomes like all members of the
Dasyuridae. This suggests that the primitive phalangers may have retained the
chromosome number and morphology of possible dasyurid ancestors but the
resemblances may be due to parallel evolution of similar chromosome number
and morphology in separate groups.
The chromosomes have been studied in more than 50% of Macropodinae.
Cytological evidence suggests that Thylogale (3 species studied), Petrogale
(2 species studied), and probably Lagorchestes (1 species studied), all with 22
chromosomes, are a related group. Onychogalea unguifer, with 20 chromosomes,
may be derived from this group. There is no justification for the placing of
Thylogale billardierii in the genus Protemnodon. Lagostrophus fasciatus has
2n = 24 and its placement in a monotypic genus is justified. Macropus major
and all species of Protentnodon, except P. bicolor, are a related group with 16
chromosomes. M. robustus is possibly included in this group. M. rufus has 20
chromosomes and should perhaps be placed in the separate genus Megaleia.
P. bicolor, with 11 chromosomes in the male and 10 in the female, differs from
all other species of Protemnodon and this genus, as at present constituted, may
be diphyletic. The relationships of P. bicolor are unknown. Setonix brachyurus
has 22, mostly metacentric, chromosomes and its affinities are at present unknown.
Three species of Bettongia (Potoroinae) have 22 chromosomes which are
mostly metacentric. Hypsiprymnodon moschatus has 22 chromosomes which
are mostly acrocentric. Both genera are very different cytologically from
Potorous tridactylus.
Estudios citogenéticos de dos especies y una variedad del género Nyctocereus (Cactaceae)