Isochromosome Y [46, X, i(Yq)] and female phenotype

A 26‐year‐old patient with female phenotype and the karyotype 46, x, i (Yq) is described. She had no breast, and a rudimentary uterus and streak gonads were present. Apart from a rather deep voice, no signs of masculinization were observed, nor did she display any of the stigmata usually associated with Turner's syndrome. The Yq chromosome was identified conclusively by the Giemsa C‐banding technique. The function of the Y chromosome is discussed briefly, and it is concluded that the factors determining or regulating somatic male differentiation must be located in the short arm of the Y chromosome.