XYY (Double Y) syndrome is a rare genetic disease where a patient receives an extra Y chromosome from the father. This results in a total of 47 inherited chromosomes instead of the usual 46.


Diagram of inheritance through meiosis


XYY syndrome is not an inherited disorder, rather it is acquired through a reproduction malfunction in the father's sperm cells (as shown above). During chromosome speration in anaphase II of meiosis II (commonly referred to as non-disjunction) can result in reproductive (sperm) cells that contain two Y chromosomes. Then, if this cell plays a roll in the fertilization of an egg, the resultant child will have this extra Y.


Victims of XYY syndrome suffer the most behaviorally, as they are often characterized by learning disabilities and anger management issues. Along with this they also suffer from accelerated growth rates and long legs that are not in proportion to the rest of the body.