Genome-wide association study is an observational study that compares DNA markers across the genome in people with a disease or trait to people without the disease or trait.
Genome is the complete set of genes or genetic material present in a cell or organism.
Genetic variants or markers are bits of DNA (i.e. the four DNA bases – A, C, G, and T) that vary from person to person.
Heterosexual behaviour in this study is defined as reporting sexual relationships only with someone of the opposite sex.
Non-heterosexual behaviour in this study is defined as having ever had a sexual relationship with someone of the same sex.
Genetic makeup refers to a person’s genetic material; the set of genes that they carry.
A correlation indicates the degree and type of relationship between two variables.
A twin study is a study in which identical and nonidentical twins are used to obtain an estimate of the heritability of a trait. Identical twins are genetically identical, whereas nonidentical twins are only 50% genetically similar. Any difference in similarity of identical vs similarity of nonidentical twin pairs can therefore be attributed to genetics.
We say that a characteristic/behaviour is heritable if a proportion of individual differences in the trait is due to genetic differences between individuals.