Scientists have uncovered a hidden clue as to why men are taller than women.
No matter where you travel in the world, men in any human population tend to be taller than women. Now, researchers have discovered a key genetic mechanism behind this anatomical contrast.
By analyzing three large public health databases, a team led by scientists at the Geisinger College of Health Sciences in Pennsylvania found 1,225 adults with unusual chromosomal combinations.
The combinations were statistically modeled in relation to the height of each adult, revealing an intriguing difference in the influence of a sequence found on both the X and Y chromosomes, known as the SHOX gene (short stature homeobox).
Unlike the X and Y chromosomes in a typical male cell, one of the two X chromosomes (known as the 'inactive' X chromosome, or Xi for short) in a typical female cell tends to function at reduced capacity to avoid complications.
The data showed that the Y chromosome delivers more of a 'SHOX effect' than the inactive X chromosome, contributing an average additional height of 3.1 centimeters (1.2 inches).
We have known for some time that the SHOX gene may be playing some role. However, this study specifically quantifies the difference in how active it is on the Y chromosome compared to the partially silenced X chromosome.
"This finding is consistent with the hypothesis that reduced expression of SHOX in women results in a net height difference between the sexes," the researchers wrote in their published article.
The researchers calculated that this difference represents 22.6 percent of the average height difference between men with XY chromosomes and women with XX chromosomes, along with other factors (including the wealth of the country you live in).
Through the three health databases used in this study (one from the UK and two from the USA), the average height difference between men and women ranged from 12.85 to 13.72 centimeters.
"These results are consistent with the hypothesis that elevated expression of SHOX on the Y chromosome compared to the Xi chromosome results in greater height among men than among women, largely explaining human sexual dimorphism in relation to height," the researchers wrote.
Height is only partially determined by genetics, with taller parents being more likely to have taller children. Hormonal levels, including testosterone (much more abundant in men than in women), are also thought to play a role in determining how tall we become.
This research could be a useful starting point for all sorts of future studies on the differences in phenotypes (observable characteristics) between the sexes, as well as diseases and disorders that affect the sexes differently.
Conditions such as Alzheimer's disease are more common in women, for example, and there likely exists a complex number of related reasons for this.
Just like with height, distinguishing between genetics and hormones could offer some useful insights.
"Untangling the effects of sex hormones from genomic variation could provide new insights into the pathogenesis of medical conditions with observed sexual discrepancies, including autoimmune, cardiovascular, and neurodevelopmental psychiatric disorders," the researchers wrote.
The research was published in PNAS.#news_update #ScienceAndTechnology #BinancelaunchpoolHuma #SaylorBTCPurchase 