Also called fraternal or non-identical twins, they are a pair of twins created by the fertilization of two eggs or ova by two separate spermatozoa at the same within the same menstrual cycle. In rare cases, it can occur within one menstrual cycle of each other. They can be of the same sex or different sexes. If they have the same father, they share about half their genes in common, and thus are no similar than any other siblings. During prenatal life, they develop in separate amnions and have their own placentae. There is evidence that dizygotic twins run in families, and thus a genetic basis for such twinning.
See Amnion (or amniotic sac), Chorion, Co-twin method, Differential parenting, Human Connectome Project (HCP), Monozygotic twins, Placenta, Zygosity