Twins that result from a single fertilized ovum are called?

• A. Monozygotic
• B. Dizygotic
• C. Conjoined
• D. Fraternal

Answer: (A)

When a single fertilized egg splits into two embryos, the result is monozygotic twins, also called identical twins. They originate from one zygote, so they share essentially the same genetic material, which is why they’re usually the same sex and look alike. The timing of that split can affect the membranes and placenta: an early division often yields two separate placentas and amniotic sacs, while a later division can lead to a shared placenta or even shared membranes, and very late splitting can result in conjoined twins. The other terms come from different scenarios: twins from two separate eggs are dizygotic or fraternal, and conjoined twins are monozygotic twins that failed to separate completely.