Customised Surface Markers for the Separation of X and Y Bearing Mammalian Sperm

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The pre-selection of offspring sex would be hugely beneficial in animal husbandry. In many farm species such as pigs or dairy cattle, female offspring are much more economically important than males, while in other species such as racehorses or beef cattle, males are preferred. For example, adult male boar meat can have an "off" flavour known as boar taint, thus making it uneconomical to raise intact male pigs to high weights. Currently, boar taint is avoided by early slaughter or castration of male pigs, which is ethically undesirable as well as economically wasteful. This project seeks to discover ways to separate sperm bearing an X chromosome (which will give females) and those bearing a Y chromosome (which will give males) before fertilisation occurs. Currently, the only way to do this is by using a dye to stain the DNA in the sperm head, and separating the sperm that have more DNA from those that have less - this works because the X chromosome is slightly larger than the Y. This "flow-sorting" process is (a) slow and cumbersome and not commercially viable for some species such as pig where large doses of semen are required for artificial insemination and (b) involves staining the DNA and shining an ultraviolet laser on it, both of which can potentially damage the DNA. There is thus a strong demand for more efficient and safer ways of separating X and Y sperm.This project aims to approach this issue by using modern molecular genetic transgenic techniques to create animals that produce sperm expressing an artificial surface marker. This will be done in such a way that either only X or Y bearing sperm have this marker on the surface. The marker can then be used to separate X or Y bearing sperm from each other. By depleting the semen of sperm that express the surface marker, this will leave an ejaculate population enriched in the sperm of the opposite sex that do not contain the artificial surface marker gene to be used to breed the next generation. In livestock, this would enable sperm selection while preventing genetically modified organisms entering the food chain.