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Term Definition

47, XXY is the way in which the karyotype of a person with Klinefelter syndrome is written. It contains information on the total number of chromosomes present as well as the sex chromosomes. Most men with KS have an extra copy of the X chromosome (47, XXY) instead of the more usual 46 chromosomes that include one X and one Y chromosome (46,XY).

This occurs as a random error during cell division to create either the egg or sperm. The chromosomes fail to separate correctly and the egg or sperm gains an extra copy of the X chromosome.

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