Gaby
In every country and in every part of the world, men are generally taller than women. Recently, scientists uncovered the reason behind this anatomical feature.
A team of researchers led by scientists from the Geisinger College of Medicine in Pennsylvania analyzed three large health databases involving 1,225 British and American adults with unusual combinations of chromosomes.
The combinations were statistically modeled based on each participant’s height, revealing a fascinating difference in the influence of the SHOX gene (short stature homeobox) on the X and Y chromosomes. (As a reminder, the male chromosome set is XY, while the female set is XX.)
Compared to the X and Y chromosomes in a typical male cell, one of the two X chromosomes in a female cell (known as the inactive X chromosome, or Xi) operates at reduced efficiency “to avoid complications.” Meanwhile, the SHOX gene is more active on the male Y chromosome, contributing approximately 3.1 centimeters to male height.
However, scientists have long known that the SHOX gene plays a significant role in bone development. This study quantitatively defined the difference in how much more it “supports” the Y chromosome compared to 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 researchers wrote in their report.
They calculated that the identified genetic mechanism accounts for 22.6 percent of the average height difference between men and women. In the case of the three studied databases, the average height difference between the sexes 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 chromosome) leads men to grow taller than women, which largely explains sexual dimorphism,” the scientists noted.
However, they also pointed out that height is not determined solely by genetics: children of tall parents are likely to be tall as well. Hormone levels also play a role in height. For instance, testosterone, which is significantly higher in men than in women, as reported by Science Alert.
This research could serve as a starting point for future studies exploring phenotypic differences between the sexes, as well as analyzing diseases and disorders that manifest differently in men and women. For example, Alzheimer’s disease, which is more commonly found in women.
“Identifying the effects of sex hormones on genomic variations allows for a new understanding of the pathogenesis of diseases with sex differences, including autoimmune, cardiovascular, and neuropsychiatric disorders,” the researchers believe. The results of this work were published in the journal PNAS.
