APA Dictionary of Psychology

twins, of the same or different sex, that have developed from two separate ova fertilized by two separate sperm. DZ twins are genetically as much alike as ordinary full siblings born as singletons, with each individual inheriting a random half of each parent’s genes. On average, DZ twins are approximately half as genetically similar to one another as monozygotic twins. For every 1,000 pregnancies, there are, on average, 7 to 12 DZ twins. Also called fraternal twins. See also twin study.