Growing sperm in a test tube may offer a powerful new way to genetically modify animals and potentially correct human genetic diseases before conception.

The technology offers two advantages. Firstly, it creates GM animals in one generation rather than two, unlike most conventional techniques.

Secondly, because the genes are spliced into laboratory-born sperm, it may allow scientists to do sophisticated genetic manipulations in a wide range of animals. So far these have only been possible in mice.

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