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?

Options

• They are monozygotic twins.

• They are fraternal twins.

• They were conceived through in-vitro fertilisation.

• They have 75% identical genetic content.

Answer 1

They are fraternal twins.

Explanation:

Twins of different sexes (a boy and a girl) must be fraternal (dizygotic) twins, because monozygotic (identical) twins always share the same genetic material and hence the same sex. Fraternal twins arise from two different eggs fertilised by two different sperms, which allows for gender variation.