Why is CCR5-Δ32 common only in Europe?
CCR5-Δ32 likely rose under strong selection and spread fast by long-range dispersal; its range is limited more by time than by southern selection barriers.
Source
The geographic spread of the CCR5 Delta32 HIV-resistance allele
Study at a glance
- Design
- Computational / modelling — Spatially explicit wave-of-advance model of CCR5-Δ32 frequency clines and allele age
- N
- Population-genetic modeling of allele frequencies — no single sample N
- Population
- Geographic CCR5-Δ32 allele-frequency data
- Outcome
- Selection and dispersal parameters explaining Δ32 geographic spread
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Why is CCR5-Δ32 common only in Europe?
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What allele was modeled?
We find the Δ32 allele is likely restricted geographically because of limited time to disperse rather than local selection pressures.
How did it attain its current range?
spread rapidly via long-range dispersal and intense selection to attain its current range.
What they did
Fit a spatially explicit wave-of-advance model to Δ32 frequency clines and allele-age estimates.
What they found
Strong selection (s≥0.1) and rapid long-range dispersal are needed; geographic restriction fits limited dispersal time better than purely local selection; origin may be outside northern Europe.
The limits
What it doesn't show
Does not definitively identify the historical selective agent (plague vs smallpox debated).
Key terms
- CCR5-Δ32
- 32-bp deletion conferring HIV resistance when homozygous.
- Wave of advance
- Spatial model of allele spread under selection and dispersal.
- Selection coefficient (s)
- Relative fitness advantage of an allele.
- Geographic cline
- Gradual allele-frequency change across space.
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Δ32 range limit mainly reflects
Common questions
What limits Δ32’s range?
Limited time to disperse more than local selection alone.
How strong was selection?
Models require s ≥ 0.1.
Where is it found?
Europe, West Asia, North Africa; north–south cline.
Selective agent settled?
No—plague proposed, smallpox also plausible.
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