What is the difference between identical and fraternal twins?

Identical twins, also known as monozygotic twins, originate from a single fertilized egg that splits into two embryos during the early stages of development. This process results in two individuals that share the same genetic material, making them genetically identical. Because they arise from the same egg and sperm, they typically have the same sex and share virtually the same DNA, which is why they often look very similar.

On the other hand, fraternal twins, or dizygotic twins, develop from two separate eggs that are fertilized by two different sperm cells. This means that each twin has its own distinct genetic make-up, similar to that of siblings born at different times. Fraternal twins can be of the same sex or different sexes, highlighting the variation in their genetic composition. Therefore, understanding that identical twins originate from one fertilized egg while fraternal twins arise from two separate eggs accurately captures the primary difference between the two types of twins.