Synaptic behaviour of sex chromosome in two XYY men.

Analysis of meiotic pairing behavior in two XYY males presenting at subfertility clinic brings evidence that the abnormal mode of pairing caused by the presence of the extra Y chromosome, disturbs achievement of spermatogenesis resulting in severe oligoastheno-teratozoospermia. In contrast, the loss of the supernumerary Y before meiosis, allows achievement and normal sperm production.