- Mutated Allele Makes Sperm Less Likely to Fertilize - Image Wikimedia Commons
Natural selection, the main driving force of evolution, tends over time to weed out mutations that cause lessened fertility in both males and females. But a recently isolated allele of the gene DEFB126 seems to lower the fertility, by as much as thirty percent, in those males who carry two copies of this allele. And startlingly, males carrying one copy of the gene may make up as much as half of the entire male population. Scientists are curious as to why a mutation that clearly lowers the possibility of offspring to such a degree could have persisted so strongly among human populations.
Protective Sperm Coating
The normal functioning allele of the DEFB126 gene works by manufacturing a protein that cloaks sperm in a carbohydrate coating in order to make it better able to maneuver through the harsh environment of the female reproductive tract, which tends to treat sperm as an invading force to be held at bay by the immune system. The mutated allele of DEFB126, however, fails to produce this coating, making the sperm more vulnerable and less likely to fertilize the egg.
Fertility Lowered by Thirty Percent
The study, published July 20th in the journal Science Translational Medicine, largely followed couples in China who had been trying to conceive, but preliminary samples from European and African populations showed a similar frequency of the mutated gene in these populations as well. Men carrying one copy of the mutated gene (estimates range as high as fifty percent of males studied) did not seem to have compromised fertility.
About twenty percent of men in the sample carried two copies of the allele and the fertility of these males appeared to be lowered by about thirty percent; thus, these men were significantly less likely to conceive a child even after two years of trying.
Causes of Infertility
Up to fourteen percent of all couples experience infertility at some point during their reproductive years. The causes of infertility are generally evenly spilt between men and women. The discovery of this new mutation, which is undectable in currently used infertility tests, may help to explain the roughly seventeen percent of infertility cases whose biological basis cannot be found. Scientists are hoping that an easily administered test will be developed to detect this mutated allele.
Why is the Mutation So Common?
Scientists are still interested as to why such an infertility allele mutation could have survived and been maintained as long as it has. While the research is still in the very early stages, experts speculate that the mutated DEFB126 gene probably confers some other undiscovered advantage that offsets the detrimental effects of the gene.
Source:
Harmon, Katherine. "Lowered Male Fertility Linked to Common Genetic Mutation." Scientific American. 20 July, 2011. Accessed on the Web. 21 July, 2011. .
Jenny Ashford - Jenny Ashford is a writer and graphic artist from central Florida. Her main area of interest in her Suite 101 articles is science, with a ...
