Genetics and Twins

The phenomenon of twinning has fascinated scientists and others over the centuries. A twin pregnancy has a higher risk of fetal morbidity and mortality than a singleton pregnancy depending on the zygosity and chorionicity of the fetuses. Dizygotic twins originate from two separate ova that are fertilized by two different sperm and are no more alike than any two siblings, and monozygotic twins develop from a single fertilized ovum, develop from one zygote, and are genetically “identical.” Recent evidence has shown that “identical twins” are more genetically discordant than originally thought because of epigenetic factors. In addition, twins are more at risk for chromosomal abnormalities and congenital anomalies. In the last century, twins played and continue to play an important role in genetics research. Twin studies are the criterion standard for research on the importance of heritability and environmental influences on behavior and disease.