Comparative cytogenetics in three species of Wood-Warblers (Aves: Passeriformes: Parulidae) reveal divergent banding patterns and chromatic heterogeneity for the W chromosome

Chromosomal rearrangements are an important process in the evolution of species. It is assumed that these rearrangements occur near repetitive sequences and heterochromatic regions. Avian karyotypes have diverse chromosomal band patterns and have been used as the parameters for phylogenetic studies. Although the group has a high diversity of species, no more than 12% has been analyzed cytogenetically, and the Parulidae family are extremely underrepresented in these studies. The aim of this study was to detect independent or simultaneous chromosomal rearrangements, and also to analyze chromosomal banding convergences and divergences of three Wood-Warblers species (Myiothlypis leucoblephara, Basileuterus culicivorus, and Setophaga pitiayumi). Our CBG-band results reveal an unusual W sex chromosome in the three studied species, containing a telomeric euchromatic region. The GTG and RBG bands identify specific regions in the macrochromosomes involved in the rearrangements. Cytogenetic data confirm the identification of speciation processes at the karyotypic of this group.

Competition Between Different Variegating Rearrangements for Limited Heterochromatic Factors in Drosophila melanogaster

Position effect variegation (PEV) results from the juxtaposition of a euchromatic gene to heterochromatin. In its new position the gene is inactivated in some cells and not in others. This mosaic expression is consistent with variability in the spread of heterochromatin from cell to cell. As many components of heterochromatin are likely to be produced in limited amounts, the spread of heterochromatin into a normally euchromatic region should be accompanied by a concomitant loss or redistribution of the protein components from other heterochromatic regions. We have shown that this is the case by simultaneously monitoring variegation of a euchromatic and a heterochromatic gene associated with a single chromosome rearrangement. Secondly, if several heterochromatic regions of the genome share limited components of heterochromatin, then some variegating rearrangements should compete for these components. We have examined this hypothesis by testing flies with combinations of two or more different variegating rearrangements. Of the nine combinations of pairs of variegating rearrangements we studied, seven showed nonreciprocal interactions. These results imply that many components of heterochromatin are both shared and present in limited amounts and that they can transfer between chromosomal sites. Consequently, even nonvariegation portions of the genome will be disrupted by re-allocation of heterochromatic proteins associated with PEV. These results have implications for models of PEV.

A physical map of the X chromosome of Drosophila melanogaster: cosmid contigs and sequence tagged sites.

A physical map of the euchromatic X chromosome of Drosophila melanogaster has been constructed by assembling contiguous arrays of cosmids that were selected by screening a library with DNA isolated from microamplified chromosomal divisions. This map, consisting of 893 cosmids, covers approximately 64% of the euchromatic part of the chromosome. In addition, 568 sequence tagged sites (STS), in aggregate representing 120 kb of sequenced DNA, were derived from selected cosmids. Most of these STSs, spaced at an average distance of approximately 35 kb along the euchromatic region of the chromosome, represent DNA tags that can be used as entry points to the fruitfly genome. Furthermore, 42 genes have been placed on the physical map, either through the hybridization of specific probes to the cosmids or through the fact that they were represented among the STSs. These provide a link between the physical and the genetic maps of D. melanogaster. Nine novel genes have been tentatively identified in Drosophila on the basis of matches between STS sequences and sequences from other species.

Variability of Euchromatic and Heterochromatic Regions of Y Chromosome in Two Types of Cancer Patients

Heteromorphism of Y chromosome was studied in head and neck cancer patients and leukemia patients. The results were compared with similar data obtained for healthy men. It was observed that, compared to the controls, mean lengths of Y chromosome were nonsignificantly higher for leukemia patients and lower for head and neck cancer patients. The euchromatic region of Y chromosome (Y-eu) remained comparable in the controls and the leukemia patients, whereas it was smaller in patients with head and neck malignancies. The heterochromatic region (Y-het) was more or less analogous in controls and head and neck cancer patients, however, it was significantly larger in patients with leukemia (P < 0.02).

CYTOGENETIC ANALYSIS OF THE cSOD MICROREGION IN DROSOPHILA MELANOGASTER

ABSTRACT This report describes the genetic organization of a euchromatic region on the third chromosome of Drosophila melanogaster extending cytologically from 68A2 to C1, an interval comprising 10 or 11 polytene chromosome bands. The gene for cytoplasmic superoxide dismutase (cSOD) maps within this interval, as does low xanthine dehydrogenase (lxd).—Recessive lethal mutations were generated within the region by ethyl methanesulfonate mutagenesis and by hybrid dysgenesis. These lethals fall into 11 functional groups, which were partially ordered by complementation with deletions having breakpoints within the region. The distribution of dysgenesis-induced mutations in the region is highly nonrandom, the majority being within a single group. The mutability of this gene is comparable to that of singed (sn), a documented "hot-spot" for P-element insertion.—One of the EMS-induced lethals, l-108, fulfills biochemical criteria expected of a hypomorphic allele of cSOD. To our knowledge this is the first such allele recovered of this gene, and it should prove very useful in an analysis of the in vivo function of cytoplasmic SOD. Indeed, it has been demonstrated that cSOD is almost certainly a vital gene.