There are two types of twins –

1. Identical or the monozygotic twins

2. Non identical or the dizygotic twins

The monozygotic or identical twins are formed by cleavage in one zygote, that is, only one fusion took place between an ovum and a sperm, a single fertilization. After this fusion, the zygote formed gets cleaved into two equal halves, leading to the formation of two identical twins. Since they are formed from a single fertilised ovum, they have same variations and thus they appear alike.

The dizygotic twins are formed by fusion of two different ova with two different sperms In a single pregnancy. This fusion leads to the formation of two different zygotes and hence two non identical twins are formed. These non identical twins can be of same or different sexes, depending on the fusion of sperms.

This was the basic difference between identical and non identical twins. I hope this helps. 😊