Trying to find out why certain physical traits between men and women differ, researchers at the University of Helsinki in Finland turned their attention to the sex chromosome shared by men and women - chromosome X - and how it might influence height.

Chromosomes are DNA-carrying structures in the nuclei of human cells. The sex chromosomes - X and Y - determine whether an embryo becomes male or female.

In each human cell, men have one X chromosome and one Y chromosome, while women have two X chromosomes. 

"Studying the X chromosome has some particular challenges," admits study author Dr. Taru Tukiainen.

A genetic variant with a role in cartridge development is more common among people who are shorter than average. This gene is much stronger in women.

But why was this gene - which is associated with a gene called "ITM2A" - more powerful in women? 

ITM2A is a chromosome X gene. Normally, one of the X chromosomes in female cells is randomly and permanently inactivated - except in egg cells. But the researchers found that ITM2A could escape this "silencing" of one of the X chromosomes.

This means that two copies of the gene could remain active in each cell in women - unlike men, who, with just one X chromosome, would only have one copy of the gene per cell.

Because the X chromosome is such an important source of DNA, the researchers hope that their work, which is published in the journal PLOS Genetics, provides motivation for future researchers to further examine this chromosome and how it influences other biological differences between men and women.

They think that such research will give scientists a better understanding of why some diseases are more prevalent in one sex than the other.