As you can see XYY syndrome is a rare genetic disorder. XYY syndrome occurs in about 1 in 1,000 newborn boys. I guess that you can say that I am lucky but I do not see it that way. Five to ten boys with XYY are born in the United States each day. Normal people have 46 chromosomes in each cell. Two of the 46 chromosomes, known as X and Y, are called sex chromosomes because they help determine whether a person will develop male or female sex characteristics. Females typically have two X chromosomes (46,XX), and males have one X chromosome and one Y chromosome. However, I have 2 Y chromosomes instead of 1.