Live-Borns from XX but Not XY Oocytes: DISCUSSION(1)

Predominant Development of Female Chimeras

In the present study, all but one (89%) of the live-born chimeras, which were composed of B6.YTIR and XX BALB/c cells in varying proportions, developed the female phenotype. The only exception was a male with bilateral testes. This strong bias towards the female sex was unexpected. When chimeric mice are composed of XX and XY cells, the XY cells usually exert a dominating effect on sexual differentiation. Singh et al. have reported that as little as 10% contribution of XY cells is sufficient to induce testis formation. ventolin inhaler

Thus, the majority of XX XY chimeras develop into males and seldom into hermaphrodites or females. In the B6.YTIR strain, the testis-determining function is partially impaired, resulting in development of adult males, hermaphrodites, and sex-reversed females at a 1:1:2 ratio. Nonetheless, if XX cells play only a passive role in gonadal sex determination, the sex ratio in XX BALB/c <-» B6.YTIR chimera would have been close to that in the nonchimeric B6.YTIR progeny. Instead, the presence of XX cells appears to have further reduced the testis-determining activity of B6.YTIR cells, since all but one chimera developed into females and none into hermaphrodites. Overall production of the putative testis-determining gene product may be critical for directing the sexual differentiation in the gonad.

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