If it works in mice, it could also work with humans
A simple, reversible chemical treatment can segregate X-bearing sperm from Y-bearing sperm, allowing dramatic alteration of the normal 50/50 male/female offspring ratio, according to a new study by Masayuki Shimada and colleagues at Hiroshima University, published in PLOS Biology.
The study was performed in mice, but the technique is likely to be widely applicable to other mammals as well, including humans.
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.
Treatment of mouse sperm with an X-retarding chemical, followed by in vitro fertilization with the fastest swimmers, led to litters that were 90% male. When the slower swimmers were used instead, the litters were 81% female.
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. This procedure could greatly simplify sex selection for either IVF or artificial insemination. Such techniques are widely used in the agricultural animal breeding field, as well as in human assisted reproduction.
The technique could prove very valuable in animal husbandry. “In a dairy farm, the value of a female dairy cow is much higher than male, because milk is only produced by female cows,” Shimada told The Guardian. “In the case of beef meat production, the speed of growing is much higher in males after castration than females.”
Michael Cook is editor of BioEdge
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