Zoology · Human Reproduction
NEET (UG) 2025 — Question 166
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?
- Option A:
They are monozygotic twins.
- Option B:Correct
They are fraternal twins.
- Option C:
They were conceived through in vitro fertilisation.
- Option D:
They have 75% identical genetic content.
Answer: B
Step-by-step solution
Monozygotic twins arise from one fertilised egg splitting into two; they are genetically identical and always of the same sex. A boy and a girl are of different sexes, so they cannot be monozygotic twins. Boy-girl twins must therefore be dizygotic (fraternal) twins, formed from two different eggs fertilised by two different sperms. Fraternal twins share on average about 50% of their genes, just like any two siblings. IVF is not a requirement for fraternal twins; twins can be conceived naturally. Thus the statement that must be true is B: They are fraternal twins.
Answer key and solution verified before publishing.
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- Exam
- NEET (UG) 2025
- Paper
- 2025 paper
- Subject
- Zoology
- Chapter
- Human Reproduction
- Topic
- Fertilisation and Implantation
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