Chromosomal Mapping of Repetitive DNAs in Myiopsitta monachus and Amazona aestiva (Psittaciformes, Psittacidae) with Emphasis on the Sex Chromosomes.

Here, for the first time, we describe the karyotype of Myiopsitta monachus (Psittacidae, Arini). We found 2n = 48, corresponding to the lowest diploid number observed in Neotropical Psittaciformes so far, with an uncommonly large W chromosome homomorphic to the Z. In order to better understand the evolution of the sex chromosomes in this species, we applied several molecular cytogenetic approaches, including C-banding, FISH mapping of repetitive DNAs (several microsatellite repeats), and whole-chromosome painting on metaphases of M. monachus. For comparison, another species belonging to the same tribe but with a smaller W chromosome (A. aestiva) was also analyzed. The results show that the constitutive heterochromatin has a very diverse distribution pattern in these species revealing heterochromatic blocks in the centromeric region of all chromosomes and in most of the length of the W chromosome in A. aestiva, while in M. monachus they were found in interstitial and telomeric regions. Concerning the microsatellites, only the sequence (CG)n produced signals on the W chromosome of A. aestiva, in the distal region of both arms. However, in M. monachus, (CAA)n, (CAG)n, and (CG)n probes were accumulated on the W chromosome, and, in addition, the sequence (CAG)n also hybridized to heterochromatic regions in macrochromosomes, as well as in microchromosomes. Based on these results, we suggest that the increase in length of the W chromosome in M. monachus is due to the amplification of repetitive elements, which highlights their significant role in the evolutionary process of sex chromosome differentiation.

Cytotaxonomic considerations on Neotropical Psittacidae birds and description of three new karyotypes.

Chromosomes obtained from feather tissues of 14 species of Brazilian Psittacidae were analyzed by Giemsa conventional staining and the karyotypes of Ara chloroptera, Propyrrhura maracana and Nandayus nenday are presented for the first time. The remaining species showed no chromosome differences when compared with previous literature data. Two basic karyotype patterns were observed. A karyotype pattern is mostly characterized by biarmed macrochromosomes, while in the other one most macrochromosomes are telocentrics.