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A 2041 bp DNA fragment isolated from the Sxr (sex reversed) region of the mouse Y Chromosome (Chr) was sequenced and characterized. The sequence, pY8/b, contains four exons that are highly similar to 525 contiguous bases from the cDNA of human ubiquitin activating enzyme El. Two of the exons contain stop codons, indicating that pY8/b is not part of a functional gene. Sequences related to pY8/b were amplified from the Y Chr of the inbred mouse strain, C57BL/6J. These sequences may be portions of the recently discovered functional equivalent of pY8/b. Despite a high degree of similarity with the human El gene, the functional equivalent of pY8/b is not the mouse El gene, because unlike El, the functional equivalent of pY8/b is expressed in a tissue-specific manner. These data are discussed with respect to theory on the evolution of the mammalian Y Chr, and in particular, to the prediction that functional genes on the Y Chr have a male-specific function. 相似文献
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The Y chromosome of the mouse is decondensed in Sertoli cells 总被引:4,自引:0,他引:4
The condensation of the Y chromosome in mouse cells was studied with two repetitive DNA probes, pY353/B and M34. Both DNA probes are specific to the Y chromosome and hybridize in situ along the whole chromosome. Due to the high resolution of the in situ hybridization technique with non-radioactive labeled DNA probes it was possible to observe the degree of condensation of the Y chromosome in the interphase cell nuclei of various somatic tissues and on testes preparations. The Sertoli cells were the only cell type in which the Y chromosome was always observed to be in a highly decondensed state. The decondensation of the Y chromosome in the Sertoli cells supports the view that the genetic activity of the Y chromosome is cell autonomous and opens the way to its molecular analysis. 相似文献
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A. G. Clark 《Genetics》1988,119(3):711-720
A theoretical population genetic model is developed to explore the consequences of X-Y recombination in the evolution of sex chromosome polymorphism. The model incorporates one sex-determining locus and one locus subject to natural selection. Both loci have two alleles, and the rate of classical meiotic recombination between the loci is r. The alleles at the sex-determining locus specify whether the chromosome is X or Y, and the alleles at the selected locus are arbitrarily labeled A and a. Natural selection is modeled as a process of differential viabilities. The system can be expressed in terms of three recurrence equations, one for the frequency of A on the X-bearing gametes produced by females, one for each of the frequency of A on the X- and Y-bearing gametes produced by males. Several special cases are examined, including X chromosome dominance and symmetric selection. Unusual equilibria are found with the two sexes having very different allele frequencies at the selected locus. A significant finding is that the allowance of recombination results in a much greater opportunity for polymorphism of the Y chromosome. Tighter linkage results in a greater likelihood for equilibria with a large difference between the sex chromosomes in allele frequency. 相似文献
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Chromosomal sex determination is phylogenetically widespread, having arisen independently in many lineages. Decades of theoretical work provide predictions about sex chromosome differentiation that are well supported by observations in both XY and ZW systems. However, the phylogenetic scope of previous work gives us a limited understanding of the pace of sex chromosome gain and loss and why Y or W chromosomes are more often lost in some lineages than others, creating XO or ZO systems. To gain phylogenetic breadth we therefore assembled a database of 4724 beetle species’ karyotypes and found substantial variation in sex chromosome systems. We used the data to estimate rates of Y chromosome gain and loss across a phylogeny of 1126 taxa estimated from seven genes. Contrary to our initial expectations, we find that highly degenerated Y chromosomes of many members of the suborder Polyphaga are rarely lost, and that cases of Y chromosome loss are strongly associated with chiasmatic segregation during male meiosis. We propose the “fragile Y” hypothesis, that recurrent selection to reduce recombination between the X and Y chromosome leads to the evolution of a small pseudoautosomal region (PAR), which, in taxa that require XY chiasmata for proper segregation during meiosis, increases the probability of aneuploid gamete production, with Y chromosome loss. This hypothesis predicts that taxa that evolve achiasmatic segregation during male meiosis will rarely lose the Y chromosome. We discuss data from mammals, which are consistent with our prediction. 相似文献
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M. F. Hammer A. B. Spurdle T. Karafet M. R. Bonner E. T. Wood A. Novelletto P. Malaspina R. J. Mitchell S. Horai T. Jenkins S. L. Zegura 《Genetics》1997,145(3):787-805
We examined variation on the nonrecombining portion of the human Y chromosome to investigate human evolution during the last 200,000 years. The Y-specific polymorphic sites included the Y Alu insertional polymorphism or ``YAP' element (DYS287), the poly(A) tail associated with the YAP element, three point mutations in close association with the YAP insertion site, an A-G polymorphic transition (DYS271), and a tetranucleotide microsatellite (DYS19). Global variation at the five bi-allelic sites (DYS271, DYS287, and the three point mutations) gave rise to five ``YAP haplotypes' in 60 populations from Africa, Europe, Asia, Australasia, and the New World (n = 1500). Combining the multi-allelic variation at the microsatellite loci (poly(A) tail and DYS19) with the YAP haplotypes resulted in a total of 27 ``combination haplotypes'. All five of the YAP haplotypes and 21 of the 27 combination haplotypes were found in African populations, which had greater haplotype diversity than did populations from other geographical locations. Only subsets of the five YAP haplotypes were found outside of Africa. Patterns of observed variation were compatible with a variety of hypotheses, including multiple human migrations and range expansions. 相似文献
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Chromosome 19 of the house mouse 总被引:2,自引:0,他引:2
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Common Mechanisms of Y Chromosome Evolution 总被引:5,自引:0,他引:5
Y chromosome evolution is characterized by the expansion of genetic inertness along the Y chromosome and changes in the chromosome
structure, especially the tendency of becoming heterochromatic. It is generally assumed that the sex chromosome pair has developed
from a pair of homologues. In an evolutionary process the proto-Y-chromosome, with a very short differential segment, develops in its final stage into a completely heterochromatic and to
a great extends genetically eroded Y chromosome. The constraints evolving the Y chromosome have been the objects of speculation
since the discovery of sex chromosomes. Several models have been suggested. We use the exceptional situation of the in Drosophila mirandato analyze the molecular process in progress involved in Y chromosome evolution. We suggest that the first steps in the switch
from a euchromatic proto-Y-chromosome into a completely heterochromatic Y chromosome are driven by the accumulation of transposable elements, especially
retrotransposons inserted along the evolving nonrecombining part of the Y chromosome. In this evolutionary process trapping
and accumulation of retrotransposons on the proto-Y-chromosome should lead to conformational changes that are responsible for successive silencing of euchromatic genes, both
intact or already mutated ones and eventually transform functionally euchromatic domains into genetically inert heterochromatin.
Accumulation of further mutations, deletions, and duplications followed by the evolution and expansion of tandem repetitive
sequence motifs of high copy number (satellite sequences) together with a few vital genes for male fertility will then represent
the final state of the degenerated Y chromosome.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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The local origin of the Tibetan pig and additional insights into the origin of Asian pigs 总被引:3,自引:0,他引:3
Yang S Zhang H Mao H Yan D Lu S Lian L Zhao G Yan Y Deng W Shi X Han S Li S Wang X Gou X 《PloS one》2011,6(12):e28215