The XYY reference article from the English Wikipedia on 24-Jul-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

XYY

XYY (or XYY Syndrome) is a trisomy in which the male receives an extra "Y" chromosome.

The incidence of this condition is about 1 per 1000 in human males. Other than being slightly taller and having more severe acne than normal, XYY males are not significantly different from "normal" males. An old study suggested that there were more XYY males incarcerated than expected, but this study has been widely countered as being procedurally flawed. There are reports that XYY men may be more likely to have behavior problems, possibly due to a higher testosterone level, but these are usually avoided if the syndrome is detected early. There are also reports of learning difficulties, but they may be caused by the behavior problems.

Since there are no distinct physical characteristics, the condition usually is only detected during genetic analysis for other reasons.

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