A group of researchers studied the data of one million people and found evidence that a stature gene shared by both sexes is amplified in men.
Men are higher than women, for an average of 13 centimeters. But why? It is not a genetic inevitability: there are many species in the tree of life in which females exceed males.
A new study, published Monday in the Journal Proceedings of the National Academy of Sciences, in which genetic data of one million people were used, has found a partial explanation.
It has to do with a gene called Shox, which is known to be associated with height. The show is present both in the X chromosome – women have two X chromosomes – and on the Y chromosome; Men have an X and a Y.
The researchers suspected that the Shox could explain the differences in stature between men and women, but there was a problem with that hypothesis. Since the show is found both on the X chromosome and in the Y, the gene would have to have a different effect on each chromosome. The researchers wondered if so.
To investigate the hypothesis, they wondered if a chromosome and additional increased the stature of a person more than an additional X chromosome.
There are unusual conditions in which people are born with an X or one and one, or one less. To find people with these conditions, the researchers consulted the data of three biobancos, or deposits of genetic and medical information of individuals. One of the biobancos was British and the other two Americans.
With the data of almost a million individuals from the biobancos, the group was able to find 1225 people with X O chromosomes and absent or leftover. It was known that some of these conditions, as in people with an X and none and, were related to health problems, as well as, in this case, with low stature.
And they discovered that an additional and more stature than an additional X. His hypothesis was confirmed.
The biochemistry of the shox gene could be the cause.
Matthew Oetjens, Geisinger College of Health Sciences from Danville, Pennsylvania, and the main author of the study, explained it in this way: the location of the Shotox gene, he said, is close to the end of the sex chromosomes. In women, most genes of one of the two x are silenced, or inactive. However, a region in which genes remain active is at the end of the X. The Shox gene is close enough to the extreme so as not to be quite silenced.
In men, the X, with its show, is totally active. There is also the Y.
This means that a woman, with her two X chromosomes, will have a slightly smaller dose of the shox gene than a man, with an X and a Y.
Consequently, men have a slightly higher effect of the SHOX gene. This, the researchers calculated, explains almost a quarter of the average difference of stature between men and women. Oetjens said that other characteristics of male sex hormones explain most of the rest of the difference, and it is believed that other genetic factors also influence.
The work is “Great, no doubt,” said Eric Schadt, professor at the Department of Genetics and Genomic Science at the Mount Sinai School of Medicine in New York.
“It is a great use of these biobancos to reveal what is still a mystery,” he said. “Although the effect is modest, it explains more or less 20 percent of the stature difference.”