Dictionary of Human Evolution and Biology

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Presence of more than the normal number of X chromosomes in the cells of an individual. All X-polysomic individuals risk the production of gametes with an unbalanced sex chromosome count. Males with 47,XXY have one Barr body, 48,XXXY have two Barr bodies, 49,XXXXY have three Barr bodies, etc. Females with 47,XXX have two Barr bodies, 48,XXXX have three Barr bodies, 49,XXXXX have four Barr bodies, etc., and progressively impaired intelligence proportional to the number of Barr bodies.

See trisomy X.

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