Most male patients with sex chromosome XYY are infertile, and only a few male patients with sex chromosome XYY are fertile.
The normal sex chromosomes in males are two xy, and when an extra y chromosome is added, a sperm-neutral chromosome abnormality develops, often resulting in azoospermia, necrospermia, or severe oligozoospermia.
The abnormal chromosomes in these sperm cannot be paired with homologous chromosomes, i.e., the sperm carrying the genetic material of the abnormal chromosomes cannot combine with a normal egg to form a fertilized egg.
Very few spouses of such men can become pregnant and should also be tested for genetic risk of the fetus through genetic counseling, chromosome testing, prenatal diagnosis and other related tests. The genetic risk of such fetuses tends to be higher, with a higher likelihood of chromosomal abnormalities, and prompt termination of pregnancy is recommended when necessary.