rs1421085
FTO, the body weight variant
What this position does
The best-known common variant affecting body weight. This particular position is the one shown experimentally to be the cause rather than merely a marker: it disrupts a control site so that developing fat cells switch towards storing energy instead of burning it.
What each result means
| If you carry | What it means |
|---|---|
| No copies of the effect version TT | You have the lower-weight version on both copies Two copies of the lower-weight-associated version. |
| One copy CT | One higher-weight copy, about a pound and a half on average Associated on average with roughly one and a half pounds more body weight. |
| Two copies CC | Two higher-weight copies, about three pounds on average Associated on average with roughly three pounds more body weight and a higher chance of being classified obese. Carriers respond to diet and exercise exactly as well as anyone else, which trials have confirmed directly. Three pounds is the largest common-variant effect on weight that exists, and it is smaller than a fortnight of holiday. |
How common each version is
| Ancestry group | C (the effect version) | |
|---|---|---|
| African | 5.6% | |
| American | 23.9% | |
| East Asian | 16.9% | |
| European | 43.2% | |
| South Asian | 30.7% |
1000 Genomes Project phase 3, via Ensembl, retrieved 2026-09-23. These groupings are coarse and flatten a great deal of internal diversity, particularly within Africa. A variant being common somewhere tells you where a piece of your ancestry probably comes from, and nothing else.
How many people carry each result
| Ancestry group | TT | CT | CC |
|---|---|---|---|
| African | 587 / 661 | 74 / 661 | 0 / 661 |
| European | 181 / 503 | 209 / 503 | 113 / 503 |
| East Asian | 355 / 504 | 128 / 504 | 21 / 504 |
| South Asian | 233 / 489 | 212 / 489 | 44 / 489 |
| American | 201 / 347 | 126 / 347 | 20 / 347 |
Counts of people, not modelled frequencies: every one of the 2,504 individuals sequenced by the 1000 Genomes Project phase 3, tallied by the genotype they carry. Deriving these from allele frequencies instead would assume random mating inside each group and undercount the homozygotes.
How to find out which you have
If you have taken a test with 23andMe, AncestryDNA, MyHeritage, Family Tree DNA, TellMeGen or Living DNA, this position is very likely already in the raw data file they gave you. You do not need another test.
One thing to watch if you look it up by hand: testing companies report some positions from one DNA strand and some from the other, and the file does not say which. Read the letters as they appear and you will get the opposite of the truth for some positions. Sequencings resolves that automatically.
Source
Coordinates and allele pair verified against Ensembl GRCh37. Direction of effect verified against VEP protein consequences or 1000 Genomes population frequency. Category: Health-adjacent.
Where this fits
Common questions
What is rs1421085?
rs1421085 is a position in the FTO gene on chromosome 16. The best-known common variant affecting body weight. This particular position is the one shown experimentally to be the cause rather than merely a marker: it disrupts a control site so that developing fat cells switch towards storing energy instead of burning it.
What does it mean if I have CC at rs1421085?
Two higher-weight copies, about three pounds on average. Associated on average with roughly three pounds more body weight and a higher chance of being classified obese. Carriers respond to diet and exercise exactly as well as anyone else, which trials have confirmed directly. Three pounds is the largest common-variant effect on weight that exists, and it is smaller than a fortnight of holiday.
What does it mean if I have TT at rs1421085?
You have the lower-weight version on both copies. Two copies of the lower-weight-associated version.
How do I find out my rs1421085 genotype?
If you have taken a home DNA test, this position is very likely in the raw data file you were given. Sequencings reads that file in your browser without uploading it, and resolves which DNA strand each position was reported from, which is the step most manual lookups get wrong.
This is reference information, not medical advice, and not a diagnosis. See the medical disclaimer. Category: Health-adjacent.