Detection of nondisjunction and recombination in meiotic and postmeiotic cells from XYSxr [XY,Tp(Y)1Ct] mice using multicolor fluorescence in situ hybridization.
Current meiotic dogma holds that synapsis is required for recombination and that recombination is required for proper disjunction. The mouse chromosome aberration XYSxr [sex reversal; redesignated XY,Tp(Y)1Ct] appears to challenge this assumption, for although chromosomes X and Y often fail to synapse and recombine, there is no dramatic increase in aneuploid progeny. An explanation of this conundrum might be that X-Y univalent spermatocytes do not survive. The phenotype of sex reversal is generated by the "obligatory" crossover between the X and Y chromosomes, which always occurs proximal to a duplicated copy of the testis-determining gene Sry and transfers one copy from one chromatid of the Y chromosome to one chromatid of the X. Animals that inherit an X chromosome with the Sry gene are chromosomally female but phenotypically male. We have used fluorescence in situ hybridization (FISH) to visualize probes for the X and Y chromosomes and for the Sry sequence and chromosome 8 to track the fate of both recombinant and nonrecombinant chromosomes through metaphases I and II into spermatids and sperm. In the 219 gametes examined by multicolor FISH, the frequency of aneuploid products (XY or "O") was low (3.7%) despite a high frequency (66%) of X-Y separation at metaphase I. In balanced gametes, X and Y recombinant chromosomes slightly exceeded nonrecombinants. Both of these observations support the earlier proposal that asynapsis and nondisjunction in primary spermatocytes lead to their developmental arrest and degeneration.
Ashley
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Department of Genetics, Yale University School of Medicine, New Haven, CT 06510.
Ried
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Ward
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D000782:Aneuploidy; D000818:Animals; D002869:Chromosome Aberrations; D015342:DNA Probes; D012734:Disorders of Sex Development; D005260:Female; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D008540:Meiosis / Q000235:genetics*; D051379:Mice; D008817:Mice, Mutant Strains; D010641:Phenotype; D011995:Recombination, Genetic; D012732:Sex Determination Analysis; D013087:Spermatids / Q000648:ultrastructure; D013094:Spermatozoa / Q000648:ultrastructure; D014960:X Chromosome; D014998:Y Chromosome
D015342:DNA Probes