Tel Aviv University researchers have genetically engineered mice to produce only female offspring, they revealed in a paper published in EMBO Reports.

While some plants, insects, crustaceans and fish can change the sex of their offspring before they are born, mammals have never before demonstrated this capability.

“The research provides the world’s first proof-of-concept for mammals to genetically produce only female progeny,” said Prof. Udi Qimron, who led the study together with Ido Yosef and Motti Gerlic, his colleagues in the Department of Clinical Microbiology and Immunology at TAU’s Sackler School of Medicine.

The researchers crossed two types of genetically engineered mice carrying specific proteins that result in a complex that halts embryonic development of males without affecting the development of females.

“Our results pave the way for a genetic system that allows biased sex production,” said Qimron.

“We proved the concept in mouse models, but the concept could also be demonstrated in other animals. We believe that the producers of cattle, swine and chicken may benefit greatly from the technology.”

He explained: “Farmers in the dairy and layer-poultry industries obviously prefer female calves and chicks, but to date, there was no accessible genetic way to regulate the sex ratio, which is naturally around 50-50. We approached this problem in an innovative way, using genetic engineering.”

This new method could provide an alternative to the practice of “culling” and killing newly hatched male chicks of egg-laying breeder hens — a practice whose cruelty spurred Yosef to seek a scientific alternative. Every year in the United States alone, about 200 million male chicks are crushed or suffocated because they are useless to the egg or meat industries.

A different Israeli approach to this problem is proposed by EggXYt, a startup developing a technology to determine the gender of chicken embryos before incubation and hatching.

Qimron emphasized that the same principles of genetic engineering that produced only female offspring among his lab’s mice could be applied to produce only males, “which are more beneficial in the beef industry.”

The research for the breakthrough study was conducted by Liat Edry-Botzer, Rea Globus, Inbar Shlomovitz and Prof. Ariel Munitz.