Scientists have developed a new sperm separation technique which could in future allow couples having IVF to choose if they have a boy or girl before fertilisation.
Experts in Japan report they have come up with a new method allowing them to split mouse sperm carrying an X chromosome from those carrying a Y chromosome.
It means sperm can be chosen based on whether they will result in female (XX) or male (XY) offspring when it is used to fertilise an egg.
It was thought the sperm of mammals that lead to both offspring are identical except for the DNA they carry.
But researchers at Hiroshima University found 492 genes are active in sperm that carry the X chromosome, which give rise to female offspring, that are not active in sperm that carry the Y chromosome, which lead to male offspring.
Some 18 of the X chromosome genes encoded receptors, and were good candidates for manipulating the sperm – because of their response to stimuli.
The team has found that a chemical that binds to two of these proteins can slow down the movement of X-carrying sperm without affecting the Y-carrying ones.
This discovery makes it easier to separate sperm according to the sex of the offspring they could produce.
Sperm from mice that were treated with the chemical, followed by in-vitro fertilisation with the fastest swimmers, led to litters that were 90% male.
This was compared to litters of 81% female when slower swimmers were used.
Scientists say that whilst other methods of separating X and Y sperm exist, they are cumbersome, expensive, and risk damaging the DNA of the sperm.
The study was performed on mice – but the technique is thought to be widely applicable to other mammals too.
Researchers say that unlike the Y chromosome, which does not carry many genes, the X chromosome carries lots, some of which remain active in the maturing sperm.
That provides a theoretical basis for distinguishing the two, the research published in the journal PLOS Biology sets out.
Professor Masayuki Shimada, said: “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 pigs by this method.
“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.”
Dr Peter Ellis, lecturer in Molecular Biology and Reproduction, University of Kent School of Biosciences, said: “This study makes the startling claim that there are cell surface markers on X- and Y-bearing sperm cells that ‘label’ these and selectively affect their function.
“This type of marker has been sought for many years in many different species, but thus far without success.
“If this study were to be replicated – and in particular if it holds true in species other than mice – then the implications could be colossal for both animal and human artificial insemination and assisted reproduction, but we are certainly not at that stage yet.”