What type of twins develop from a single fertilized egg that splits in two, resulting in genetically identical organisms?

Identical twins, also known as monozygotic twins, develop from a single fertilized egg that undergoes division into two separate embryos. This process occurs very early in development, typically within the first few days after fertilization. Because both embryos originate from the same fertilized egg, they share the exact same genetic material, making them genetically identical to one another.

This genetic similarity is why identical twins often have the same physical traits and may exhibit similar behaviors and personality traits. The splitting of the fertilized egg can happen at various stages of development, leading to variations in the twins' situations, such as whether they share a placenta or have separate placentas, which can influence their prenatal environment.

In contrast, fraternal twins, also called dizygotic twins, arise from two separate eggs being fertilized by two separate sperm cells, resulting in siblings that are genetically similar like any other siblings but not identical. Other options like polar twins and half-siblings do not pertain to the formation of twins from a single fertilized egg.