Twins produced from a single fertilized ovum are called identical twins. The two cells resulting from the first cleavage of the zygote separate and develop into independent embryos. They have the same chromosome set in their body cells and thus possess identical genes.
They are identical in every respect and it is difficult to differentiate between them.
What are fraternal twins
Twins produced from two different fertilization are called fraternal twins. When two separate ova are fertilized by two separate sperms two zygotes having different sets of genes are obtained they are not identical to each other.
They differ from each other in their traits, development and Often sex.