Gaby
Men are generally taller than women in every country and region. Recently, scientists uncovered a genetic reason behind that difference.
A team led by researchers at Geisinger College of Medicine in Pennsylvania analyzed three large health databases that included 1,225 British and American adults with unusual chromosome combinations.
The researchers statistically modeled those combinations against each participant’s height and found a striking difference in how the SHOX gene (short stature homeobox) acts on the X and Y chromosomes. (Male chromosomes are XY; female chromosomes are XX.)
In female cells, one of the two X chromosomes—the inactive X, or Xi—is partially silenced to prevent problems, so it works less efficiently. Meanwhile, SHOX is more active on the Y chromosome and adds about 3.1 centimeters to male height.
Scientists have long known that SHOX plays an important role in bone development. This study measured how much more SHOX is expressed from the Y chromosome than from the partially silenced X chromosome.
“This discovery aligns with the hypothesis that reduced SHOX expression in women leads to the overall height difference between the sexes,” the authors wrote.
They calculated that this genetic mechanism explains 22.6 percent of the average height gap between men and women. Across the three databases, the average sex difference in height ranged from 12.85 to 13.72 centimeters. “These results support the theory that increased SHOX expression on the Y chromosome compared to the Xi leads men to grow taller than women, which largely explains sexual dimorphism,” the authors added.
But height isn’t determined only by genes: children of tall parents are likely to be tall too. Hormones also affect growth. For example, Science Alert reported that testosterone is significantly higher in men than in women.
The researchers say this work could kick off studies into other physical differences between the sexes and into diseases that affect men and women differently. For example, Alzheimer’s disease is more common in women.
“Identifying the effects of sex hormones on genomic variation offers a new way to understand the development of diseases with sex differences, including autoimmune, cardiovascular, and neuropsychiatric disorders,” the authors wrote. The results appeared in PNAS.
