Genome-wide association study

A genome-wide association study tests genetic variants across many people for statistical associations with a trait or disease. It can identify genomic regions linked to a phenotype but does not by itself establish causation.

Single-nucleotide polymorphism: A DNA position where individuals commonly differ by one nucleotide. Many studies test these common variants as markers across the genome.
Genotype: The genetic variants carried by an individual at one or more loci. A study compares participants’ genotypes with their measured traits.
Polygenic risk score: A score combining many genetic variants, weighted by their estimated associations with a trait. Genome-wide association estimates supply the variant weights used to build many scores.
Genome-wide linkage study: A genetic study that tracks co-inheritance of genomic regions within families to locate trait-associated loci. Linkage uses family inheritance patterns, unlike association tests across population samples.
Linkage disequilibrium: The nonrandom association of alleles at different genetic loci in a population. A significant marker can signal a nearby causal variant because inherited alleles travel together.
Phenotype: An observable or measurable characteristic of an organism, shaped by genetic and environmental factors. The phenotype defines the outcome or trait whose genetic associations are tested.
Mendelian randomization: A method that uses genetic variants as instrumental variables to investigate causal effects of exposures. Association findings can provide instruments, though their assumptions require separate scrutiny.
Candidate gene study: A study testing selected genes chosen in advance for possible links to a trait or disease. It tests a narrow, preselected set rather than scanning variants across the genome.
Genome-wide significance: A statistical threshold designed to limit false-positive findings across many genetic tests. Testing hundreds of thousands of variants requires a much stricter threshold than a single test.
Allele frequency: The proportion of copies of a genetic variant among chromosomes in a population. Variant frequency affects statistical power and the interpretation of association results.

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