International researchers have reported the first complete analysis of the X-chromosome, which is linked to more than 300 diseases.
The findings in two studies published this week in the British journal Nature might explain how the X chromosome determines the differences between men and women.
Chromosomes are microscopic coils of genetic information located in each cell of every living thing.
Humans have 22 pairs of chromosomes plus the gender chromosomes, X and Y, each inherited from one of their parents. Women have two X chromosomes, while men have an X and a Y.
The researchers say it appears that women's genes appear to work harder than men's to influence the fate of both genders.
They found evidence that 75 percent of the time, before it is born the healthy female body switches off one copy of its X-chromosome that might cause disease.
Researcher Laura Carrel of Penn State College of Medicine in Hershey, Pennsylvania says usually, there is no problem in women whose bad genes do not switch off.
"For others, though, it brings up a new intriguing possibility that these are contributing to particular disorders, potentially in how they are manifested, potentially in how they progress, how they respond to particular treatments," she explained. "And so this would give us kind of new avenues to look at in looking at diseases that seem to affect males differently than females or that tend to have different variability in females."
In men there is nothing to switch off. So an abnormal copy of an X-protein might explain why certain X-linked diseases, such as hemophilia and Duchenne's muscular dystrophy, are only seen in men.
Researchers also mapped the locations of genes on the X and Y chromosomes. The study of the human genetic material is expected to help understand the causes and aid diagnosis and treatment of inherited ailments, including mental retardation, testicular cancer, and immune system disorders.
Members of the research team were from the Wellcome Trust Sanger Institute, Baylor College of Medicine in Houston, Texas; the Max Planck Institute for Molecular Genetics and the Institute for Molecular Biotechnology in Germany; and the Washington University Genome Sequencing Center in St. Louis, Missouri.