A new and reversible chemical treatment was found to segregate X-bearing sperm from Y-bearing sperm, stated new study by Masayuki Shimada and colleagues at Hiroshima University, published in the open-access journal PLOS Biology. The study was performed in mice, but the technique is likely to be widely applicable to other mammals as well.
Most cells from male mammals contain both an X and a Y chromosome, but during sperm development (spermatogenesis), the X and Y chromosomes are segregated into different cells so that an individual sperm will carry either one or the other, with an X chromosome giving rise to daughters and a Y chromosome to sons.
Unlike the Y chromosome, which carries very few genes, the X chromosome carries many, some of which remain active in the maturing sperm. This difference in gene expression between X- and Y-bearing sperm provides a theoretical basis for distinguishing the two.
There are other procedures that can be used to separate X and Y sperm, but they are cumbersome, expensive, and risk damaging the DNA of the sperm. The procedure developed by these authors has the potential to greatly simplify sex selection for either in vitro fertilization (in which sperm and egg join in a lab dish) or artificial insemination (in which sperm are implanted into the female reproductive tract). Such techniques are widely used in the agricultural animal breeding field, as well as in human assisted reproduction.
"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," Shimada said. "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."