Which type of twins are formed from a single zygote that splits into two embryos?

Identical twins, also known as monozygotic twins, are formed from a single zygote that undergoes division to create two separate embryos. This splitting typically occurs in the early stages of development, shortly after fertilization, which results in each embryo having the same genetic material, thereby making them genetically identical.

This genetic similarity is the reason why identical twins often share the same physical characteristics and are often indistinguishable from one another. In contrast, other types of twins, such as fraternal (dizygotic) twins, originate from two separate zygotes fertilized by two different sperm cells, leading to two genetically unique individuals. The term "heterozygous twins" does not accurately describe any type of twin formation and is not commonly used in this context. Therefore, the correct understanding of twin formation clearly identifies identical twins as the result of a single zygote dividing into two embryos.