Up until a few short decades ago when ultrasound imagery became sharp enough to reveal the relevant details, parents had to wait for the arrival of a new family member to learn its gender. Could a day come when they're not only aware of this at the point of conception, but have the final say in whether it's a boy or a girl? A significant breakthrough in genetics research out of Japan has raised this very question, with scientists establishing a new kind of chemical treatment that can produce mice litters made up mostly of a desired sex.

The work was carried out by scientists at Hiroshima University, who were on the hunt for biomarkers that could be used to distinguish X chromosomes from Y chromosomes, which are carried by individual sperm, with the former producing female offspring and the latter leading to male offspring.

Telling one from the other ahead of fertilization has historically proven difficult, but the Hiroshima University scientists claim to have now teased out some very useful differences. According to an analysis in mice, the X chromosome carries many more genes than the Y chromosome. They were able to identify around 500 of these that were active and unique to the X-bearing sperm and not to be found in the Y chromosome.

Of those 500 active genes, the team learned that 18 of those encode receptors that could serve as potential targets to dampen the swimming abilities of sperm carrying the female DNA. This led them to a chemical treatment that targeted two of these receptors in particular, and proved successful in applying the brakes to the sperm's motility.

Applying the technique to mouse sperm led to sperm traveling at different paces, in effect separating the X-chromosome-carrying swimmers from those carrying the Y-chromosome. Using the faster group for in vitro fertilization led to a litter of mice that were 90 percent male. Using the slower-swimming group instead, the litter wound up being 81 percent female. Far from perfect, but also far from the 50/50 split we've come to expect over hundreds of thousands years of human history.

"The differential expression of receptor genes by the two sex chromosomes provides the basis for a novel and potentially highly useful method for separating X and Y sperm and we have already succeeded the selectively production of male or female in cattle and pig by this method," says Masayuki Shimada, study co-author.

As Shimada touches on there, gender preselection for livestock is an active area of research and one with important consequences concerning the environment and food security. Male cows, for example, yield greater quantities of meat per carcass than female, but current methods can be expensive and risk damage to the DNA.

This new method, according to the authors of the study, could offer a much simpler solution for use in in vitro fertilization and artificial insemination, techniques already widely used in livestock breeding practices. Regarding humans, the team believes that the technology would be "widely applicable" to other mammals, but do urge caution in this regard.

"Nonetheless, use of this method in human reproductive technology is speculative at the moment, and involves significant ethical issues unaffected by the utility of this new technique," says Shimada.

The research was published in the journal PLOS Biology.

Source: PLOS via ScienceDirect