In December 2022, researchers developed a technique in which single-sex litters could be created. The proof of principle research was reported in Nature Communications, and was used to generate litters of mice that were either only female or only male. In both scientific research and agriculture, there are often situations in which a specific sex is required, and the other sex is irrelevant or unneeded. Sex differences can confound some research studies, so for years, many scientists have focused their research on males. In agriculture, only female animals are used in dairy and in egg production. These stipulations result in the culling of billons of animals every year. This research, and other new work could help change that.
Scientists at the Francis Crick Institute and the University of Kent designed a CRISPR system in two parts, one of which is contributed by the mother and the other can be contributed by the father. The system targeted the Top1 gene, which is required for DNA repair and replication.
When the two parts of the CRISPR-Cas9 system come together in an embryo, it stops developing at the 16- to 32-cell stage. Since the mother carries two X chromosomes, all of her offspring carry one part of the CRISPR system. Fathers are designed to carry the other portion of the CRISPR system on either their X or their Y chromosome. If it's on the father's X chromosome, then all of the female offspring of the litter would carry both parts of the CRISPR system, and would stop developing; a male-only litter would be created. But if the father carries the other portion of the CRISPR system on his Y chromosome, then male offspring would stop developing and a female-only litter would be produced.
This method worked 100 percent of the time to produce sex-specific litters.
Another group of scientists has also made progress in ending the culling of male chicks in agriculture by creating hens that lay eggs in which only females hatch. Billions of male chicks are slaughtered every year because these animals do not lay eggs and cannot serve any other purpose.
This work has not been published because the scientists are working on licensing it for agriculture. That also means that other researchers have not been able to assess their data or the validity of their claims. But the technology seems to have also worked with gene editing. The edited hens, called Golda hens, lay eggs that are then exposed to blue light for a few hours. This light exposure halts the development of male chick embryos. The blue light does not affect female embryos, who go on to develop normally. How soon these techniques might be brought to agriculture remains to be seen, but some countries like Germany, are already starting to take steps to limit or halt the culling of male chicks, which could make the adoption of the technology inevitable.
Sources: The Francis Crick Institute, BBC, Nature Communications