Question

why are identical twins always of the same sex but fraternal twins may or may not be of the same sex?​

Answer 1

HEY -:)

Identical twins are also called as monozygotic twins. They are derived from a single zygote that splits at an early stage during development. They have same genetic make up and are of the same sex.

Dizygotic (fraternal) twins are produced in the rare case when two ova are released simultaneously. They are fertilized by two different sperms. Each fertilized ovum develops into an embryo. It could be of the same sex or the different sex and they are genetically dissimilar. 

Answer 2

Explanation:

this Is because identical twins are result of sepration of a single zygote .

but the faternal twins are the result are result of two zygotes fertilized at the same time making them squire diff. characters . thus they may or may not be of same sex