The difference between identical and fraternal twins is based on how they are formed from the fertilized eggs. Identical twins are formed when one fertilized egg splits into two embryos, while fraternal twins are formed when two different eggs are fertilized by two different sperm. Identical twins have the same genetic information, while fraternal twins share about 50% of their genes, just like any other siblings. Identical twins usually look very similar and have the same sex, while fraternal twins can look different and have different sexes¹