Abstract: A construct which allows animals to be bred in captivity but renders them infertile in the wild by allowing reversible control over fertility and reproduction. The construct comprises: a first promoter that is activated in a defined spatial (tissue specific) or temporal manner linked to DNA encoding a transactivating protein; and a second promoter, which is activated by the transacting protein, linked to DNA encoding a blocker molecule which disrupts gametogenesis or embryogenesis. Feeding an animal a molecule that prevents the transactivating protein binding the second promoter controls fertility.

Abstract: The invention provides a nucleic acid construct, which may be inserted into the genome of a target organism. The construct consists of a promoter that is activated during the sex-determining stage of embryonic development/or gametogenesis, and a blocker that inhibits expression of a gene critical for sex differentiation.