Twins and twinning

© 2019 Elsevier Inc. All rights reserved. This chapter reviews research involving twins from historical studies to the current molecular era, what we know and what we don’t know about the twinning process for typical and atypical twins, the incidence and influences on twinning, twin designs and analytical approaches, and how researchers and twins can interact to enhance twin research. Notable additions to the previous edition include the use of twins for studies of epigenetics (microbiome, (clinical trials), twin zygosity determination and testing, twin registries and collaborations, and more detailed sections on twin research designs, etiology of twinning, and genetic and epigenetic differences within monozygotic twin pairs.