Population stratification

Population stratification is a term used in genetic epidemiology to describe a situation where apparent association between a gene and a disease is actually due to a systematic difference in allele frequencies between subpopulations. This can lead to spurious association in case-control studies.

Overview

Population stratification occurs when a population is composed of subgroups with different allele frequencies. This can occur due to genetic drift, founder effect, or population bottleneck. If these subgroups also differ in disease prevalence, this can lead to spurious associations in genetic association studies.

Causes

The main causes of population stratification are genetic drift, founder effect, and population bottleneck.

Genetic drift is a change in allele frequencies due to random sampling. It can lead to population stratification when different subpopulations experience different patterns of genetic drift.

The founder effect occurs when a new population is established by a small number of individuals. If these individuals have different allele frequencies than the original population, this can lead to population stratification.

A population bottleneck occurs when a population's size is reduced for at least one generation. If the surviving individuals have different allele frequencies than the original population, this can lead to population stratification.

Impact on Genetic Association Studies

Population stratification can lead to spurious associations in genetic association studies. This occurs when the allele frequencies in the case and control groups are different not because of an association with the disease, but because of differences in the subpopulation structure.

Methods to Control for Population Stratification

Several methods have been developed to control for population stratification in genetic association studies. These include genomic control, structured association, and principal components analysis.

Genomic control is a method that uses a set of unlinked markers to estimate the degree of population stratification and then adjusts the test statistics accordingly.

Structured association is a method that uses genetic data to infer the population structure and then includes this as a covariate in the association analysis.

Principal components analysis is a method that uses genetic data to identify the major axes of genetic variation and then includes these as covariates in the association analysis.

See Also

• Genetic association
• Genetic drift
• Founder effect
• Population bottleneck
• Genomic control
• Structured association
• Principal components analysis

Population stratification Resources
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