Genetic mapping of the polled/intersex locus (PIS) in goats

Sex determination in mammals is due to a complex cascade of gene regulations involving SRY and autosomal and X genes. Study of intersex cases in domestic mammals could enlighten some parts of this basic developmental pathway and therefore clarify the mechanisms of sexual differentiation in humans, especially for autosomal mutations affecting non Y-downstream sex-determining genes. Intersex condition is well documented in dairy goats. It is due to a recessive gene which is associated with the dominant autosomal gene for hornlessness, P. In the homozygous state, the P gene causes masculinization of all polled genetic females PP. The study of 13 polled intersex goats permitted to describe in detail the external morphology, anatomy of the reproductive tract, gonadal histology and chromosomal constitution. All animals exhibited two inguinally located udders. Seven of them appeared to be closer to the female phenotype on the basis of general conformation, external and internal genitalia while the other six had the general appearance and internal reproductive tract resembling males. The gonads of all animals contained seminiferous tubules lined by Sertoli cells. No germ cells were observed. The chromosome analyses of the blood and gonadal cultures prepared from each animal showed a normal female karyotype (2n = 60,XX). No Y chromosome was observed in any of the metaphase spreads. Furthermore, using PAR amplification and Southern blot, no DNA specific sequence of the Y chromosome (SRY and ZFY) was detected. A linkage analysis within 12 pedigrees segregating for the polled trait allowed the localization of the polled/intersex locus in the distal region of goat chromosome 1. According to comparative mapping data, no sex-determining gene has been described so far in the human homologous region. This genetic localization constitutes the first step towards the identification of a new autosomal sex determining gene in mammals.