Topic: Sex determination: humans, birds, honey bee· Genetics and Evolution

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?

1. They are monozygotic twins.

2. They are fraternal twins.

3. They were conceived through in vitro fertilization.

4. They have 75% identical genetic content.

Doubtly Asked 30 Oct 2026 NEET UG 2025 Practice test neet Save WhatsApp Report

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Answer: 2. They are fraternal twins.

Key idea: Monozygotic twins come from one zygote and have the same sex.

A boy and a girl have different sex, so they must come from two different eggs fertilised by two sperms: fraternal (dizygotic) twins. IVF is not required, and 75% identical is not a fixed fact (fraternal twins share about 50% on average). Option 2.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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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?

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