Klinefelter syndrome, 47, XXY, or XXY syndrome is a genetic disorder where people have an extra number of X chromosomes. People who have Klinefelter's Syndrome are often called "XXY Males", or "47, XXY Males".[dead link]
In other organismsEdit
Other males can have Klinefelter's Syndrome as well as humans. The mouse is one example. Tortoiseshell or calico markings on male cats are an indicator of a similar syndrome. These cats are considered to be the model organism for Klinefelter syndrome, because the gene for a cat's tabby coat markings is found on the X chromosome. 
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