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XYY syndrome

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A genetic condition wherein a male has an extra Y chromosome


In humans, the sex chromosomes are the X chromosome and the Y chromosome. The basis of sex determination in humans is on the pair of sex chromosomes present in an individual. For instance, females have a pair of two X chromosomes whereas males have one X chromosome and one Y chromosome. There are instances though when certain individuals have a different set of sex chromosomes. For example, an extra Y chromosome in a male is an indication of XYY syndrome.

XYY syndrome is a genetic condition in which the male is born with an extra Y chromosome. Thus, males with XYY syndrome would have 47 chromosomes and a 47, XYY karyotype. One possible cause could be traced back to a nondisjunction during anaphase II of spermatogenesis. There are also cases wherein the extra Y chromosome is due to a nondisjunction during a post-zygotic mitosis.1

Symptoms are few and the person with this condition may not be aware of it especially that they generally have normal fertility. Some of the common symptoms with XYY syndrome include being exceptionally tall, (about 6 ft or taller), prone to acne, and learning difficulties.

Also called:

  • YY syndrome
  • Jacobs syndrome
  • double Y syndrome

See also:

1 Robinson, D. O. and Jacobs, P. A. (November 1, 1999). "The origin of the extra Y chromosome in males with a 47,XYY karyotype". Hum Mol Genet. 8 (12): 2205–2209.