A CRISPR-based technique has been used in mice to ensure they give birth to exclusively female offspring. This has applications for selecting the sex ratio in livestock.

Although offspring sex selection through genetic techniques has previously been achieved in fish and insects, this is the first successful attempt in mammals. Mammal offspring sex selection has previously relied upon sperm selection. As this is an expensive and time-consuming technique it is not widely used. The CRISPR method represents a much more accessible alternative.

Both parent mice were genetically engineered. The maternal mouse encoded the CRISPR associated Cas9 protein and the paternal mouse encoded guide RNAs on its Y chromosome. The Cas9 protein is inactive unless it is programmed by guide RNAs. After fertilisation the Cas9 and guide RNAs were only combined in the male embryos, as the female embryos lack the Y chromosome. The Cas9 protein was therefore able to selectively eliminate the male embryos in-vivo, ensuring only female embryos were born.

The CRISPR technique is therefore able to halt development of male embryos without impacting the development of female embryos.

Selecting for female embryos is extremely useful for egg-laying and dairy based industries. The scientists state that the system could be reconfigured to ensure only male offspring, which is more useful for the beef industry. It is possible that selecting for female embryos could prevent animal cruelty, as male chicks are often killed at birth.

Once refined, the CRISPR technique has the potential to revolutionise livestock production.

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