rs2814778
Duffy-null: the strongest population difference in the human genome
What this position does
Plasmodium vivax malaria gets into red blood cells through the Duffy protein. A single change switches that protein off in red cells, and the parasite loses its doorway. It sits above 95 per cent across West and Central Africa and near zero in Europe and Asia, which makes it the most sharply differentiated common variant known in our species.
Blood. Shaped by vivax malaria, over thousands of years in africa. This is one of the variants that differs sharply between human populations, because something in the environment made one version worth having.
Infection, and the cost of fighting it
For most of human history the commonest way to die young was infection. An immune system tuned to win those fights is tuned for a world that, in rich countries, no longer exists.
What changed: Industry, roughly the last two centuries. Indoor work, heated buildings, refined food, cheap salt and sugar, tobacco at scale, and a collapse in infectious disease. This is where most of the deals in your genome came undone.
Why it spread: well established. The environmental pressure behind this variant is documented and not in serious dispute.
Spiral Staircase, chapter 37: The Individual Variable Spiral Staircase is written by the same author as this site.
What each result means
| If you carry | What it means |
|---|---|
| No copies of the effect version TT | You have the Duffy protein on red cells The usual result outside Africa. Red cells carry the Duffy protein. |
| One copy CT | You carry one copy of the null version One copy. Red cells still carry the protein, so the malaria resistance is partial at most. |
| Two copies CC | Duffy-null: your red cells do not carry the protein This is the result with real clinical consequences today, and they have nothing to do with malaria. Duffy-null people run a lower white blood cell count, which is completely normal for them. Measured against a reference range built almost entirely from Europeans, it reads as neutropenia. People have been referred for bone marrow biopsies, and turned away from chemotherapy and from clinical trials, over a number that was never abnormal for them. If a doctor ever tells you your white count is low, this is worth mentioning. |
Worth knowing. Duffy-null protects against vivax malaria specifically, not against falciparum, which causes most severe malaria in Africa.
How common each version is
| Ancestry group | C (the effect version) | |
|---|---|---|
| African | 96.4% | |
| American | 7.8% | |
| East Asian | 0.0% | |
| European | 0.6% | |
| South Asian | 0.0% |
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 | 4 / 661 | 40 / 661 | 617 / 661 |
| European | 497 / 503 | 6 / 503 | 0 / 503 |
| East Asian | 504 / 504 | 0 / 504 | 0 / 504 |
| South Asian | 489 / 489 | 0 / 489 | 0 / 489 |
| American | 299 / 347 | 42 / 347 | 6 / 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: Population adaptation.
Where this fits
Common questions
What is rs2814778?
rs2814778 is a position in the ACKR1 gene on chromosome 1. Plasmodium vivax malaria gets into red blood cells through the Duffy protein. A single change switches that protein off in red cells, and the parasite loses its doorway. It sits above 95 per cent across West and Central Africa and near zero in Europe and Asia, which makes it the most sharply differentiated common variant known in our species.
What does it mean if I have CC at rs2814778?
Duffy-null: your red cells do not carry the protein. This is the result with real clinical consequences today, and they have nothing to do with malaria. Duffy-null people run a lower white blood cell count, which is completely normal for them. Measured against a reference range built almost entirely from Europeans, it reads as neutropenia. People have been referred for bone marrow biopsies, and turned away from chemotherapy and from clinical trials, over a number that was never abnormal for them. If a doctor ever tells you your white count is low, this is worth mentioning.
What does it mean if I have TT at rs2814778?
You have the Duffy protein on red cells. The usual result outside Africa. Red cells carry the Duffy protein.
How do I find out my rs2814778 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: Population adaptation.