Jacobs syndrome is inherited when a baby boy receives two Y chromosomes instead of one, resulting in XYY instead of the normal XY. Jacobs syndrome is an example of an aneuploidy, a male with Jacobs syndrome or XYY syndrome has an extra chromosome meaning he will have 47 instead of 46, the abnormality is located on the 23rd pair of chromosomes aka the sex chromosomes. The cause of XYY syndrome is a random mix up during the creation of a man's genetic code.