Question

what happens when a person has a chromosome xxyy

Answer 1

48,XXYY syndrome, is an abnormality in human males in which they are having an extra copy of X and Y chromosome. This means that the affected males have 48 chromosomes instead of the typical 46 (considered normal number of chromosomes in humans).
This additional copy of X and Y chromosome in males causes delayed sexual development, sterility, undescended testes, low muscle tone, low testosterone levels etc.