Mitochondrial DNA analysis of ancient sheep from Altai.

A comparative analysis of the genetic diversity of ancient and modern sheep can shed light on the origin of these animals and their distribution as well as help to evaluate the role of humans at each formation stage of different sheep breeds. Here we isolated ancient DNA and performed sequencing of the mitochondrial DNA D-loop from 17 sheep bone remains (~4000-1000 years old) found in the archaeological complexes in the south of Altai (Western Siberia). The length of the sequences obtained ranged between 318 and 586 bp. The haplotype diversity and nucleotide diversity were 0.801 ± 0.081 and 0.0096 ± 0.0014 respectively. The average number of nucleotide differences was ~3.1. Nucleotide sequence analysis revealed that 15 specimens were nested within previously described A,B,C,D and E lineages and that two specimens had a basal position relative to the rest of the analyzed samples. A relatively high diversity of sheep haplotypes, including the presence of two basal haplotypes, indicates that the Altai region may have been a transport route of human migration. Further ancient DNA analysis of other specimens and deeper genome sequencing of samples with novel haplotypes is needed to better understand the demographic history of sheep in Southern Siberia.

New insights into sex chromosome evolution in anole lizards (Reptilia, Dactyloidae).

Anoles are a clade of iguanian lizards that underwent an extensive radiation between 125 and 65 million years ago. Their karyotypes show wide variation in diploid number spanning from 26 (Anolis evermanni) to 44 (A. insolitus). This chromosomal variation involves their sex chromosomes, ranging from simple systems (XX/XY), with heterochromosomes represented by either micro- or macrochromosomes, to multiple systems (X1X1X2X2/X1X2Y). Here, for the first time, the homology relationships of sex chromosomes have been investigated in nine anole lizards at the whole chromosome level. Cross-species chromosome painting using sex chromosome paints from A. carolinensis, Ctenonotus pogus and Norops sagrei and gene mapping of X-linked genes demonstrated that the anole ancestral sex chromosome system constituted by microchromosomes is retained in all the species with the ancestral karyotype (2n = 36, 12 macro- and 24 microchromosomes). On the contrary, species with a derived karyotype, namely those belonging to genera Ctenonotus and Norops, show a series of rearrangements (fusions/fissions) involving autosomes/microchromosomes that led to the formation of their current sex chromosome systems. These results demonstrate that different autosomes were involved in translocations with sex chromosomes in closely related lineages of anole lizards and that several sequential microautosome/sex chromosome fusions lead to a remarkable increase in size of Norops sagrei sex chromosomes.

DIVERSITY OF SEX DETERMINING MECHANISMS IN RAY-FINNED FISHES (ACTINOPTERYGII).

Ray-finned fishes (Actinopterygii) is a very diverse and numerous clade of vertebrates. Besides the diversity of ecological niches and morphology, species of this clade have substantial differences in mechanisms of sex determination. Unfortunately, our modern knowledge about sex determining mechanisms is limited to a small number of species. Even from the modest number of published works on this topic it is obvious that evolution of sex determining system in ray-finned fishes is very plastic: in some closely related species sex systems can be significantly different, there are taxa with quite conservative systems, and the same genomic loci may play sex determination role independently in various groups. Such diversity allows considering ray-finned fishes to be used as a convenient model taxon for researching emergence and development of different sex determining systems.

[Genomic structure and sex determination in squamate reptiles].

Squamata is the largest reptilian order including snakes and lizards which occupies a key position in phylogeny of amniotes. A variety of sex determination modes in lizards is one of the most interesting parts of the biology of this order. These mechanisms are genomic sex determination (both XY and ZW systems) and temperature-dependent sex determination. Studies of squamata sex chromosomes are pivotal for understanding evolution of other vertebrate sex chromosomes. Unfortunately, this clade has long been neglected by molecular geneticists. In this paper, we describe recent data on molecular cytogenetics and genomics of squamates, evolution of their sex chromosomes and sex determination mechanisms.