The gonads of the true hermaphrodites are usually streak-like, composite organs called ovotestes. An ovotestis has both ovarian and testicular tissue, suggesting the development of both cortex and medulla of the indifferent gonad. In true hermaphrodites the phenotype may be male or female but the external genitalia are ambiguous. In 70% of the cases of true hermaphroditism the genotype is 46 XX. About 20% of the cases are mosaics (46, XX / 46, XY; 45, X / 46, XY; or 46, XX / 47 XXY), and nearly 10% have 46, XY chromosome constitution.
It is easy to explain the presence of true hermaphroditism in mosaic individuals. In such persons the ovarian tissue develops from cells without a Y chromosome, whereas testicular tissue develops from cells with a Y chromosomes.
It is difficult to explain the presence of true hermaphroditism in individuals with 46, XX and 46, XY genetic constitution. It is thought that true hermaphrodites with a 46, XY genotype may also be mosaics. It has been proposed that one of the X chromosomes in some cells of these persons carries a fragment of the shot arm of the Y chromosome. These cells lead to the development of testicular tissue, whereas the normal cells cause the development of ovaries tissue. True hermaphrodites with a 46, XY genotype are the most difficult to explain. It has been suggested that in such individual some sells undergo mutation on the sex-determining region of the Y chromosome. This produces an effective mosaicism in which the mutated cells cause the development of ovaries tissue, while the normal cells lead to the formation of testicular tissue.