For meat animal husbandry
Editing a bull's embryo will turn half of its female offspring into males
Vasily Zaitsev, N+1
Geneticists managed to edit the bull embryo in such a way that males dominated its offspring, which was achieved with the help of directed insertion of a transgene. The SRY gene was inserted into chromosome 17, which should cause at least half of the embryos with genotype XX to develop along the male path. Report by Owen et al. The production of a Gene Knock-In Bull Calf by Embryo-Mediated Genome Editing was presented on July 23 at a meeting of the American Society of Animal Sciences.
Modern animal husbandry has almost everywhere moved away from keeping free herds with a natural population, some of which are sent for meat, and some produce milk. Instead, there are separate industries, the two largest of which are meat and dairy. Animals reproduce in them almost exclusively artificially, and therefore it would be advantageous to subordinate the sexual balance of the calves being born to man. Bulls are more valuable for the meat industry, because they gain weight more efficiently when consuming the same calories, and their meat is tastier and can be used to make expensive steaks. However, by nature, the ratio of male and female offspring in cows is approximately equal.
In most mammals, in a normal situation, males have sex chromosomes XY, and females - XX. Strictly speaking, it is not the Y itself that is important, but the presence of the SRY gene on it, responsible for male development. If SRY is on any other chromosome, the embryo will become a male. For example, a similar pattern is observed in people with de la Chapelle syndrome who have a female genotype XX, but a male organism, which is considered a pathology, since it inevitably leads to infertility.
Joey Owen from the University of California and her colleagues decided to achieve a more favorable sexual balance of cows. First they tried to transplant the SRY gene into the X chromosome, which would lead to offspring consisting only of males. After this failed, the researchers chose a different chromosome, 17 – the authors claim that this is the safest and most reliable option.
As a rule, the process of homologous recombination in somatic cells with subsequent cloning is used for targeted insertion of a transgene – in other words, operations are performed not with the embryo itself, but with a cell culture, the nuclei from which are then planted into the egg. Here, scientists injected CRISPR/Cas9 reagents and donor HMEJ vectors directly into the zygote (the first stage of the embryo) 6 hours after fertilization.
As a result, the Cosmo bull was born, in the offspring of which, according to the calculations of the authors of the study, there should be about 75 percent of bulls.
This is due to the fact that when crossed with ordinary cows, the SRY gene will not be inherited every time, but only in half of the cases. As a result, half of the offspring will be natural bulls with genotype XY, and 25 percent will carry genotype XX, but have an organism of males. It is worth adding that neither Cosmo nor its immediate descendants will end up in a butcher shop: the rules for genetically modified meat are very strict, and it will be released to the market only after numerous inspections and certifications.
GMO products do not cause any harm, but they have many advantages. For example, thanks to her, calves became resistant to tuberculosis, lost their horns, and rice, which is not afraid of pests, did not lose its yield.
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