Reproduction

Genetic analysis of XX-male bovine reveals tetragametic chimera

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Abstract

A Holstein bull from an elite genetic line showed up as an XX female in routine 50K SNP Chip analysis of both hair, and subsequently ear tissue. Lymphocytes from his blood were cultured, harvested, and prepared according to conventional cell culture methods and revealed a normal 60,XX karyotype with no numerical or structural chromosomal aberrations. PCR analyses were negative for the SRY gene, and positive for androgen receptor (AR) gene on the X chromosome. This bull presented as a phenotypically androgynous animal with a penis, cryptorchidism with one small (16 cm scrotal circumference) descended testicle, well defined hip bones and rib cage along with a tall straight stance, usually associated with female individuals. No sperm were found in seminal fluid collected in a routine breeding soundness exam at 17 months of age. The bull was slaughtered at 18 months of age, and his reproductive tract was collected. The small descended testicle weighed 18.9 g, and the undescended testicle weighed 42.4 g. Two very enlarged vesicular glands (43.4 g and 52.5 g, normally ~ 20 g) were observed alongside what appeared to be uterine tissue. Histology showed no tubular grooves in the ampulla, and the urethra was extremely feminized and resembled the cell lining of the uterus, with clear myometrial, endometrial, and perimetrial-like cells. Hormonal monitoring revealed the notable absence of the testosterone peak typical of pubescent males. DNA was isolated from both liver and kidney from the bull, and both blood of his dam and sperm of his sire. PacBio sequencing analysis of the case's kidney revealed presence of a Y chromosome at approximately half the read-depth of the X, and X-chromosomal reads with genetics specific to both his dam and sire. Further qPCR analysis comparing the relative abundance of AR on the X chromosome normalized to SRY on the Y indicated a ratio of 3.0 (± 0.2) X: 1.0 (± 0.08) Y ratio in the kidney and a 13.8 (± 0.03) X: 1.0 (±0.01) Y in the liver. DNA was also analyzed with 35 short tandem repeat and two sex linked markers. Parentage was confirmed. Sex linked markers were consistent with qPCR data. In the liver sample, only the X peak was clearly detected, however there was evidence of Y peak but it was below the threshold normally applied to call the presence of a Y chromosome. In the kidney sample, both X and Y alleles were detected, however the Y allele intensity was lower than the X. Moreover, genetic profiles of the two tissues were not identical, and specifically three alleles were detected for five markers in the kidney DNA. Collectively, these data suggest this bull was a mosaic tetragametic chimera resulting from the fusion of two zygotes.

Keywords: 2026

How to Cite:

Werry, N., Angove, M., Trott, J., Turner, Z., Shokrof, M., Monsour, T. A., Conley, A., Bellone, R., McNabb, B., Tatar, N., Oppenheim, S. & Van Eenennaam, A., (2026) “Genetic analysis of XX-male bovine reveals tetragametic chimera”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2295257. doi: https://doi.org/10.31274/wcgalp.24335

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