Which of the following is NOT a characteristic of fraternal twins?

• A. A single ovum has divided into two embryos.
• B. They will be the same sex.
• C. They are more likely to occur in younger women.
• D. There are two placentas.

Answer: (A)

Fraternal twins, or dizygotic twins, come from two separate eggs fertilized by two separate sperm. This means two zygotes develop, usually with two placentas, and the twins can be either the same sex or different sexes since their genetic makeup comes from two independent ova. The statement that describes a single ovum dividing into two embryos is not a feature of fraternal twinning; that process is how identical (monozygotic) twins form, where one fertilized egg splits into two genetically identical individuals. The other aspects—two placentas and the possibility of same or different sexes—fit fraternal twins.