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Genetics — Population and Quantitative

Hardy-Weinberg, QTL analysis, and evolutionary population genetics

A
allele_freq_af 25 terms Jan 14, 2026
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Terms 25

1
Hardy-Weinberg Equilibrium
p² + 2pq + q² = 1; allele/genotype frequencies stable without evolution
2
HWE Assumptions
Random mating, no mutation, no selection, no gene flow, large population (no drift)
3
Allele Frequency
Proportion of a specific allele in the gene pool; p + q = 1 for two alleles
4
Genetic Drift
Random fluctuation in allele frequencies; greater effect in small populations
5
Bottleneck Effect
Sharp population reduction causes loss of allelic diversity; alters allele frequencies randomly
6
Founder Effect
New population established by few individuals; subset of original variation; e.g. Amish, Ashkenazi Jews
7
Effective Population Size (Ne)
Idealized population size with same genetic drift as real population; often << census size
8
Selection Coefficient (s)
Measure of fitness disadvantage; fitness of genotype = 1 − s
9
Directional Selection
Consistently favors one extreme phenotype; shifts mean; reduces variation
10
Stabilizing Selection
Favors intermediate phenotypes; reduces variation without shifting mean
11
Disruptive Selection
Favors extreme phenotypes over intermediate; increases variance; can drive speciation
12
Balancing Selection
Maintains multiple alleles; heterozygote advantage (sickle cell) or frequency-dependent selection
13
Heterozygote Advantage
Heterozygotes have higher fitness than either homozygote; maintains both alleles
14
Molecular Clock
DNA mutates at roughly constant rate; used to date evolutionary divergence
15
Neutral Theory
Kimura: most molecular variation is neutral; genetic drift, not selection, drives substitutions
16
Quantitative Trait
Phenotype with continuous variation; determined by many loci plus environment
17
Heritability (h²)
Proportion of phenotypic variance due to genetic variance; h² = V_G/V_P
18
Narrow-sense Heritability
h² = V_A/V_P; only additive genetic variance; predicts response to selection
19
Polygenic Inheritance
Trait controlled by many genes each with small effect; e.g. height, intelligence, skin color
20
QTL (Quantitative Trait Locus)
Genomic region associated with variation in quantitative trait; identified by linkage mapping or GWAS
21
Linkage Disequilibrium (LD)
Non-random association of alleles at different loci; decays over generations by recombination
22
GWAS
Genome-Wide Association Study; tests millions of SNPs for association with traits or disease
23
Gene-Environment Interaction (GxE)
Effect of genotype differs across environments; reaction norm
24
Epistasis
Interaction between genes where one masks or modifies effect of another
25
Inbreeding Coefficient (F)
Probability that two alleles in an individual are identical by descent; F = 0 outbred, F = 1 fully inbred