Men are taller than women on average, and the usual answer is “hormones”. A 2025 PNAS study asks how much of the gap sits in the sex chromosomes themselves. Its answer is a little under a quarter, and the route runs through a gene called SHOX.
Source: Berry et al. (senior author Matthew Oetjens), PNAS 122(22), 19 May 2025, “X and Y gene dosage effects are primary contributors to human sexual dimorphism: The case of height”. Evidence level: abstract, UK Biobank record and the Geisinger release. The full text was not independently reviewed.
The data and the clever comparison
The team drew on genetic data from 928,605 people in three large biobanks in the United States and the United Kingdom. Among them were 1,225 adults with an extra or missing sex chromosome, such as 47,XXY, 47,XYY, 47,XXX and 45,X. These people are the key to the design.
People with an extra Y chromosome were taller than people with an extra X. A unit increase in Y dosage added about 3.1 cm more height than a unit increase in X dosage, and the authors report this independent of hormonal variables. That is how the design separates the chromosome effect from the effect of male hormones.
Where SHOX comes in
SHOX lies on both the X and the Y chromosome. Women have two X chromosomes, and one is mostly inactive, so the gene is only partly active in their cells. Men carry one X and one Y, and both copies of the gene are fully active. The authors frame the height gap against the hypothesis that reduced SHOX expression in females produces a net difference in stature.
In their analysis, the larger effect of the Y chromosome explained 22.6% of the observed height difference between XY males and XX females. Some press reports round that to nearly 25 percent, but the paper’s figure is 22.6%. The rest likely comes from other genes and from male sex hormones, as Oetjens notes.
What the height gap does and does not show
These are averages for large samples, and the two sexes overlap heavily. So nobody can read an individual’s height from their sex or from one gene. Height also depends on nutrition, childhood disease and the secular trend. That is why populations with identical gene effects can still differ in mean stature.
Using it in UPSC Mains
Paper I, clause 9.6 covers age, sex and population variation as genetic markers, and clause 10 covers factors affecting growth and development. The study is a concrete case of sex variation with a genetic basis, so it fits an answer on how genes and hormones interact in growth. Pair it with an environmental factor to keep the answer balanced.
The closest PYQ is genetico-environmental factors in human growth (2019, Paper 1), where the SHOX study supplies the genetic half of the answer. More questions are on the human genetics and human biology topic page. Related reading: the full optional guide and human biological adaptation to climate.
Sources
UK Biobank publication record; Geisinger release (AZoLifeSciences); PubMed Central article page.