Peer-reviewed veterinary case report
A sporadic case of the sex-reversed mare (64,XY; SRY-negative): molecular and cytogenetic studies of the Y chromosome.
- Journal:
- Theriogenology
- Year:
- 2003
- Authors:
- Bugno, Monika et al.
- Affiliation:
- Department of Immuno and Cytogenetics
- Species:
- horse
Plain-English summary
In this study, researchers looked at a mare (a female horse) that had a rare condition called sex-reversal syndrome, which means she had male chromosomes (64,XY) but appeared female. This mare did not have the SRY gene, which is important for male development, and her ovaries were very small, while her external genitalia looked normal. The scientists found that the mare had some genes typically found on the Y chromosome, but they also detected genes from the X chromosome, suggesting a mix-up during the formation of her father's sperm. The study suggests that this mix-up happened when the X and Y chromosomes exchanged parts during sperm development. Overall, the findings help explain how this unusual condition occurs in horses.
Abstract
A sex-reversal syndrome appears frequently in the horse. The mare carriers of this syndrome lack of SRY gene. It is suggested that sex-reversal syndrome is probably caused by transfer of the SRY gene from Y to the X chromosome, due to abnormal meiotic exchange. The aim of the study was molecular analysis of the Y-linked genes in a case of the sex-reversed infertile mare with 64,XY karyotype. The karyotype was established on the basis of analysis of 350 metaphase spreads stained by CBG banding. Molecular analysis of the loci assigned to the Y chromosome revealed absence of the SRY gene and presence of the other studied loci (ZFY, AMEL-Y and STS-Y). In this animal all fragments representing X chromosome (ZFX, AMEL-X and STS-X) were detected. External genitalia in the mare were normal, uterus was small and ovaries (examined by ultrasonography) extremely small. The mechanism of sex-reversal syndrome formation was discussed. It is postulated that during spermatogenesis in the sire two crossing-over events between the X and Y chromosomes occurred. One of them took place between the ZFY and SRY loci and another one between the SRY locus and the centromere.
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Search related cases →Original publication: https://pubmed.ncbi.nlm.nih.gov/12559464/