Account for the following briefly:

Twins may or may not be identical.

Identical twins:

1. Identical twins also called monozygotic twins, result from the fertilization of a single egg by a single sperm, the fertilized egg then splits into two.
2. Identical twins share the same genomes and are always of the same sex.

Non-identical twins or fraternal twins:

1. If two separate eggs are fertilized by two sperms, then they are dizygotic in nature and the result is non-identical or fraternal twins.
2. They typically are non-identical, and don’t have to be the same gender.

Hence, if the fertilization is monozygotic then they are identical, if the fertilization is dizygotic then they are non-identical twins.