On the origin and frequency of Y chromosome deletions responsible for severe male infertility.

The origin of deletions associated with non-obstructive severe oligozoospermia in men are discussed. Deletions could arise during various stages of meiosis, at later stages in spermatids, or post-fertilization. Certain embryonic stages may be highly sensitive. The possibilities of an inherited propensity to these and other deletions, and of mosaicism in embryos are assessed.