The Role of Sex Chromosome Chimerism in Altering Sexual Development of Mammals

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Abstract
Thirteen bovine females, twins to males, were examined in a study of the variability of the freemartin syndrome. The range of intersexuality was from foreshortened uterine horns in the least masculine to complete absence of Müllerian derivatives and development of accessory sex glands in the most masculine. Histological examination revealed no follicular development in the gonads, although juvenile ovarian stroma or testicular tissue or both were present in some. The animals were rated by the degree of masculinization of the reproductive system, which was found to be positively correlated (r = 0.70, p < 0.01) with the percentage of cells of male origin in cultures of peripheral blood from the freematins. The relevancy of these and other data to the general problem of sexual differentiation is discussed. It is concluded that the primary etiological factor of gonadal modification in freemartins is the presence of Y chromosome-bearing cells at the time of differentiation.