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Israeli scientists find way to engineer the sex of offspring in mammals


Dave Wild (CC BY-NC 2.0)

John Burger - published on 07/04/19

CRISPR technology can help farmers avoid having to kill off offspring of the wrong gender.

If you’re a poultry farmer and your business relies heavily on the sale of eggs, it’s not going to help you all that much to have a lot of roosters around. And if you’re selling milk, you don’t need a lot of bulls. According to Udi Qimron of Tel Aviv University, billions of chickens are killed annually by chicken egg farmers who had no use for so many male chicks.

The number of male calves being killed right after birth is high on dairy farms because it is cheaper to kill them than to rear them, according to the Jerusalem Post. And on beef farms, the opposite is true, where female cows are killed in favor of hefty male cattle.

A colleague of Qimron’s complained that the practice was “so cruel and unfair” that “there must be a way to overcome this.“

He and a team in the Department of Clinical Microbiology and Immunology at Tel Aviv University’s Sackler School of Medicine have found a way to put new CRISPR genome-editing technology to work to significantly reduce the chance of animals giving birth to live offspring of an “undesired” sex.

The research for the study, led by Qimron, was published on July 1 in EMBO Reports. The technology would involve the killing of embryos of one sex or the other. explaied how it works:

The researchers crossed two types of genetically engineered mice. The maternal mouse encoded a Cas9 protein, a CRISPR-protein that is inactive unless guided by special “guide-RNAs.” The paternal mouse encoded these guide-RNAs on the Y-sex chromosome, a sex chromosome present only in males. After fertilization, the guide-RNAs from the paternal sperm and the Cas9 protein from the maternal egg were combined in the male mouse embryos, but not in the female embryos (because the females lack the Y chromosome). The combination of guide-RNAs with Cas9 results in a complex that eliminates the male embryos. “We showed that Cas9 was specifically activated only in male embryos,” says Prof. Qimron. “Our results pave the way for a genetic system that allows biased sex production. When two transgenic types of mice encoding Cas9 or Y-chromosome-encoded guide-RNAs are crossed, lethality of males occurs because Cas9 is guided from the Y chromosome to target essential genes. This does not happen in females because the Y chromosome is not transferred to them. This cross thus halts embryonic development of males without affecting the development of females. “Importantly, the system can also be used to produce only males. Engineering the guide-RNAs on the paternal X-sex chromosome should result in the exclusive elimination of females, resulting in males-only progeny, which are more beneficial in the beef industry.”

Qimron said the concept could ultimately be applied to human children. “If a mad ruler decides he wants to engineer the people to have only male or female offspring,” he said, “we have provided the proof of concept.”

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