Hardy-Weinberg Equilibrium
Definition
A condition in a population where genotype frequencies at a single locus conform to expectations derived from allele frequencies alone, assuming random mating. Testing for Hardy-Weinberg equilibrium at each locus is one of the standard validation checks for forensic DNA databases.
- Applies to
- Genotype frequencies at a single locus
- Assumption
- Random mating in the population
- Basis
- Derived from allele frequencies
- Forensic use
- Standard validation check for DNA databases
Common questions
Why does a forensic DNA database get tested against Hardy-Weinberg equilibrium?+
A locus that deviates significantly from equilibrium can signal population substructure, genotyping error, or database contamination, so the test acts as a quality check on the allele frequency data used in match statistics.
What happens statistically if a locus fails the equilibrium test?+
Analysts may investigate the cause, apply a correction factor to match probability calculations, or in some frameworks exclude or flag that locus rather than use its raw frequencies uncritically.
Does deviation from equilibrium always mean something is wrong with the data?+
Not necessarily, since real populations with even modest substructure or non-random mating can show mild deviation naturally, so a statistically significant result prompts further review rather than automatic rejection.
Related terms
- Conditional Probability
- The probability of event A given that event B has already occurred, written P(A|B). Conditional probability is the basis of the multiplication...
- Linkage Disequilibrium
- The non-random association of alleles at different loci within a population. Certain HLA allele combinations (e.g., HLA-A1 with HLA-B8 with HLA-DR3) occur...
- Multiplication Rule
- For any two events: P(A and B) = P(A) x P(B|A). When A and B are independent, this simplifies to P(A) x...
- Positive Dependence
- Events are positively dependent when the occurrence of one increases the probability of the other: P(A|B) > P(A). In this case P(A...
- Statistical Independence
- Events A and B are independent if P(A|B) = P(A), equivalently P(A and B) = P(A) x P(B). Knowing B occurred gives...