Question

Twins are born to a family that lives next door to you. The twins are a boy and a girl. Which of the following must be true?

• A. They are fraternal twins.
• B. They were conceived through in vitro fertilization.
• C. They have 75\% identical genetic content.
• D. They are monozygotic twins.

Hint:

Different sexes = Fraternal twins. Same sex = Could be identical or fraternal.

Answer 1

The Correct Option is A

Monozygotic (identical) twins develop from a single fertilized egg that splits into two embryos. Since they originate from the same zygote, they are always the same sex. Dizygotic (fraternal) twins develop from two separate eggs fertilized by two different sperm. Because they are from separate zygotes, they can be different sexes and have different genetic makeup (like any siblings). A boy and a girl twin pair can only be fraternal twins. In vitro fertilization doesn't determine whether twins are monozygotic or dizygotic. 75\% genetic similarity is not a standard measure for twins.