Table 1.

A glossary of genetic terms used in this review

Familial aggregation	The clustering of certain traits, behaviors, or disorders within a given family, which are usually caused by genetic or environmental similarities
Genetic architecture	Description of the number of genetic variants, allelic frequencies, and effect sizes of variants that affect a trait and their mode of gene action
Heritability h2	The proportion of observed differences in a trait among individuals of a population that is due to genetic differences or genetic factors. The most commonly used formula is the one for narrow-sense heritability, which means the additive genetic portion of the phenotype variance and is calculated as the variance of additive effect divided by the total phenotypic variance in a population
GWAS	Genome-wide association study: a study design in which hundreds of thousands of genetic variants in the genome (usually SNPs) are tested for association with the trait
SNP	Single-nucleotide polymorphism, which is a DNA variation occurring within a population in which a single nucleotide (A, T, C, G) differs between members of a biological species
Genetic risk score	Multi-locus profiles of genetic risk, which can be used to translate discoveries from genome-wide association studies into tools for population health research
Minor allele frequency	The frequency at which the least common allele occurs in a given population
Intrapair analysis	The analysis of intrapair differences on measures within monozygotic or dizygotic twin pairs
h2SNP	The proportion of the phenotypic variance explained by the common SNPs in human genome
Missing heritability	Defined as the fact that individual genes cannot account for much of the heritability of disease, behaviors, and other phenotypes
Genetic covariance	The genetic part of the covariance, which can be used to calculate genetic correlation by standardizing the genetic variance-covariance matrix
Genetic correlation	The proportion of variance that two traits share due to genetic cause, which indicates how much of the genetic influence on two traits is common to both
Pleiotropy	Referring to one gene influencing multiple, seemingly unrelated phenotypes, which means that a mutation in a pleiotropic gene may have an effect on multiple traits simultaneously