Abstract: A method of sex selection in non-human animals is disclosed which comprises transgenic manipulation of the male to modify, destroy or identify gametes having one of either the X or Y chromosome. A chimeric construct comprising a post-meiotic regulatory region in operative association with a sex selection gene is targeted to one of either a Y or X chromosome in the genome of a male animal. The post-meiotic regulatory region may be transition protein 1 promoter. The selection sequence may be a direct or indirect mediator, or a detectable marker. An example of a direct mediator is the Rnase, Barnase. An example of an indirect mediator is the herpes simplex virus thymidine kinase gene, which forms a toxic metabolite in the presence of gancyclovir. Alternatively, a transcriptional activator protein may be linked to the post-meiotic regulatory element and the direct or indirect mediator may be linked to a promoter having a binding site specific for the transcriptional activator.