An extra X chromosome in addition to the usual male (XY) chromosome complement (47 ,XXY) has been associated with the abnormal male syndrome described (in 1942) by
H.F. Klinefelter and known as
Klinefelter syndrome. Presumably, the XXY male is produced due to fertilization of a exceptional XX egg by a Y sperm or of an X egg by an exceptional XY sperm.
Klinefelter syndrome is estimated to occur in 1 per 500 live male births. Individuals with this syndrome are phenotypically males, but with some tendency toward femaleness particularly in secondary sex characteristics. Such features as enlarged breasts (gynecomastia), underdeveloped (or sparse) body hair, small testes, and small prostate glands are a part of the Klinefelter syndrome. Tall stature, longer arms, infertility, problem in speech development ( i.e., higher pitched voice) and abnormal behaviour are also associated with this syndrome.
