The medical syndrome in which males inherit one or more extra X chromosomes. They are likely to have relatively high-pitched voices, asexual to feminine body contours as well as breast enlargement, and comparatively little facial and body hair. They usually are sterile or nearly so, and their testes and prostate gland are small. As a result, they produce relatively small amounts of testosterone.

The medical syndrome in which females inherit three X chromosomes. As adults, these women are usually an inch or so taller than average with unusually long legs and slender torsos, but otherwise appear normal. They have normal development of sexual characteristics and are fertile.

The medical syndrome in which females inherit only one X chromosome. If they survive to birth, these girls have abnormal growth patterns. They are short in stature, averaging 4 feet 7 inches as adults. They generally lack prominent female secondary sexual characteristics. They have exceptionally small, widely spaced breasts, broad shield-shaped chests, and turned-out elbows. Their ovaries do not develop normally and they do not ovulate. The few oöcytes that they produce are destroyed by the time they are two.

The medical syndrome in which males inherit an extra Y chromosome. As adults, these "super-males" are usually tall (above 6 feet) and generally appear and act normal. However, they produce high levels of testosterone. During adolescence they often are slender, have severe facial acne, and are poorly coordinated. They are usually fertile and lead normal lives as adults. Many, if not most, are unaware that they have a chromosomal abnormality.

The general term for a structural modification of a chromosome in which a portion of a chromatid is broken off and attached to a different location on that chromosome or on another chromosome. This occurs as a result of crossing-over when chromosomes are being duplicated.