Abstract
The Y chromosome in mammals is variable, even in closely related species. Middle East blind mole rats Nannospalax ehrenbergi demonstrate autosomal variability, which probably leads to speciation. Here, we compare the mitotic and meiotic chromosomes of mole rats. For the first time, we studied the behavior of their sex chromosomes in the meiotic prophase I using electron microscopy and immunocytochemical analysis. Unexpectedly, the sex chromosomes of the 52- and 60-chromosome forms of mole rats showed different synaptic and recombination patterns due to distinct locations of the centromeres on the Y chromosomes. The absence of recombination in the 60-chromosome form, the asymmetric synapsis, and the short-term disturbance in the synaptic co-orientation of the telomeric regions of the X and Y chromosomes were revealed as specific features of mole rat sex bivalents. We suggest several scenarios of Y chromosome alteration in connection with species differentiation in mole rats.
Highlights
Sex chromosomes are highly specialized elements of the genome that differ from autosomes in terms of specific gene contents, distinct behavior in meiosis, and a variety of evolutionary paths [1]
The size, morphology, and G- and C-banding patterns of the sex chromosomes of the mitotic spreads were similar in all Israeli chromosomal forms
We believe that the presence of a recombination nodule and a central element in the asymmetric SC of the mole rat sex bivalent indicates at least a partial homology of these segments
Summary
Sex chromosomes are highly specialized elements of the genome that differ from autosomes in terms of specific gene contents, distinct behavior in meiosis, and a variety of evolutionary paths [1]. Sex chromosomes demonstrate an amazing diversity in animals [2], in mammals [3,4,5]. A genetic linkage for male-specific genes was selected as soon as male-determining genes emerged on a proto-Y chromosome [11,12,13,14,15]. The dark side of the specialization appeared to be a deficiency in recombination due to the absence of homological regions between X and Y chromosomes, the declining force of natural selection, accumulating deleterious mutations, and further degradation
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