The secret of the difference in the height of men and women is a gene on the X chromosome

More chromosomes – less growth

Nadezhda Markina, "Newspaper.Ru"

Scientists have accidentally found out the genetic reasons why, on average, men are taller than women. The key turned out to be in a gene that inhibits the growth of cartilage and is located on the X chromosome. Women have two X chromosomes, so the gene makes it twice as strong.

Researchers from the University of Helsinki, understanding the genetic causes of differences in the health of men and women, simultaneously answered another question – why men are mostly higher than women. It turned out that the whole point is in the X chromosome, more precisely, that in women it is in a double copy, and in men it is in a single one. Geneticists have just started digging into the "X-file" (in the Russian version – the series "X-Files"), as they say, and expect to find a lot more interesting things in it.

Genetic variations in the X chromosome were studied by Finnish scientists in a population of 25 thousand Finns and Swedes. In their DNA, the so–called single nucleotide polymorphisms (SNP) were studied - point mutations expressed in the replacement of one nucleotide, the smallest element in the DNA structure, by another. In the X chromosome, they counted 2.6% of such variations.

The initial task was to find variations associated with an increased risk of various diseases. The second task is to find genetic factors that explain body weight, height, blood pressure and lipid profile. Along the way, they investigated the contribution of the X chromosome to the manifestation of well-known differences in male and female appearance. For example, the fact that in any ethnic group, the height of the average man is always greater than the height of the average woman.

To date, scientists have known hundreds of genes associated with appearance traits, but when studying them, the X chromosome, as a rule, was left out. She is well known for her contribution to some hereditary diseases such as hemophilia, which leads to their much greater spread in men who do not have a "spare" chromosome.

In the study, the results of which the authors described in the journal PLOS Genetics (Tukiainen et al., Chromosome X-Wide Association Study Identifies Loci for Fasting Insulin and Height and Evidence for Incomplete Dosage Compensation), they found the ITM2A gene located on the X chromosome, variants of which determine greater or lesser growth. This is because the gene is involved in the development of cartilage tissue. The longer the cartilage tissue develops, the taller a person grows.

The variant of the gene that leads to its increased work, as scientists have shown, is accompanied by stunting. That is, the intensive work of the gene at a certain level blocks the development of cartilage tissue. But in women, this gene always works more intensively than in men, because in women it is in two copies, on two X chromosomes. This is the reason that the growth of women is slowed down faster. This happens at a certain age period. It is known that in younger adolescence, at 11-12 years, girls are not lower, and often even higher than boys. But from the age of fourteen, boys begin to grow rapidly and overtake their peers.

"A double dose of X-chromosomal genes in women can cause problems during development," explains Professor Samuli Ripatti, head of the study. – To avoid this, there is a mechanism in female cells that silences the second X chromosome. But next to the ITM2A gene, we found a site that allows this gene to avoid suppression of work. When we found him, it especially inspired us."

This allows the X-chromosomal ITM2A gene to continue to work in double volume in female cells, and women stop growing because of this.

It is possible that some other genes use the same mechanism. If they avoid suppression, then women work twice as hard as men. It is quite possible that this can explain not only the growth, but also other characteristic differences between the sexes.

Scientists emphasize that the study of the X chromosome is especially interesting. This is a unique case when women and men have an unequal number of genes responsible for the same functions. At the same time, in genome-wide association studies, insufficient attention is paid to this chromosome, where quite a lot of genes are located.

"We expect that the discovery of the X-file will bring us many more biological surprises," says Dr. Taru Tuklainen, the first author of the article.

Portal "Eternal youth" http://vechnayamolodost.ru10.02.2014