CBSE Class 10 Answered

Sometimes, two eggs are released from the ovaries at a time and both may get fertilised. Such twins are called fraternal twins. They are biologically known as diovular or dizygotic twins. Since they are fertilised separately, the twins are non-identical.      

Sometimes, a single fertilised egg may split during the early stages of cell division. Such twins are called identical or monozygotic twins. Such twins are both, boys or both girls. They are very similar, but their fingerprints, birth marks and handwriting are not similar. Since they are formed from a single fertilised egg, the twins are non-identical.