Аннотация:Recombination rate and crossover distribution along chromosomes
vary considerably between the animal species. Several hypotheses
explaining this variation were developed. However, most data on re-
combination patterns were obtained from mammals. The variation in
recombination is strongly dependent on karyotypic diversity of the
species comprising this taxon.
Squamate reptiles present a good model to study recombination due
to more conservative karyotypes. Using immunolocalization of
SYCP3, the protein of the axial elements of synaptonemal complex;
MLH1, the mismatch-repair protein associated with the mature re-
combination nodules; and the centromere proteins we investigated
chromosome synapsis and recombination at pachytene in two
closely related species of iguanian lizards: the toad-headed agamas
Phrynocephalus guttatus and Ph. alpherakii.
The karyotypes of the studied specimens consisted of 23 acrocentric
bivalents: 12 pairs of macrochromosomes and 11 pairs of microchro-
mosomes (2n = 46 FN = 46). Average SC length was equal to 223.9 ±
31.7 mkm (compared to 140–150 mkm in Anolis, another iguanian).
We found that the toad-headed agamas show very high recombin-
ation rates, on average 50.1 ± 17.5 MLH1 foci per cell (compared to
21–22 in Anolis). The distribution of the crossovers along the chro-
mosomes was almost even, not showing centromere effect and inter-
ference. This is in strict contrast with other vertebrates, which show
prominent peaks of recombination near the telomeres and a de-
crease in recombination near the centromere.
This intense and evenly distributed recombination would lead to very
low linkage disequilibrium in the population, efficient selection, and
high genetic diversity. These lizards live in very harsh desert condi-
tions. Perhaps high recombination serves to ensure efficient adapta-
tion to their extreme habitat.