X- and Y-chromosomal gene expression during spermatogenesis, studied in the context of separation of X and Y spermatozoa

Mankind has been interested in S6X preselection since ancient times. Methods presumed to achieve sex preselection have already been described by Greek philosophers as far as 500 B.C. (reviewed by Betteridge, 1984). Although it took almost 2500 years since then to develop reliable and repeatable methods, sex preselection is now possible and is actually applied in both humans and livestock. It can be achieved either by sexing of early embryos or by separation of X and Y chromosome-bearing spermatozoa (X and Y spermatozoa).