Types of twins

Scientists are very interested in twins because it helps us identify the differences between genetic and environmental factors that influence health and behaviour. As a result, there’s been a lot of research on them, and this has uncovered some unusual types of twinning… such as sesquizygotic twins. Most twins are monozygotic (identical: they come from a single egg that split in two), or dizygotic (non-identical or fraternal: they come from two eggs that were released by their mother at the...