Fraternal twins in humans are produced when

Options

A. Two sperms fertilize an ovum and the first two blastomeres seprate from each other.
B. One sperm fertilize an ovum and the first two blastmeres separate from each other.
C. Egg develop parthenogenetically and first two blastomeres separte from each other
D. Two ova are fertilized simultaneously.

Answer

**Step-by-Step Solution:**

1. **Understanding Fraternal Twins**: Fraternal twins, also known as dizygotic twins, occur when two separate eggs (ova) are fertilized by two different sperm cells.

2. **Fertilization Process**: In the case of fraternal twins, two eggs are released during the same menstrual cycle and are fertilized simultaneously by two separate sperm. This results in the formation of two distinct zygotes.

3. **Development of Zygotes**: Each zygote develops independently into its own embryo. Since they originate from two different eggs and sperm, they will have different genetic makeups, unlike identical twins (monozygotic twins), which come from a single fertilized egg that splits into two.

4. **Implantation**: Both embryos implant into the uterine wall at the same time, leading to the development of two separate placentas and amniotic sacs.

5. **Conclusion**: Therefore, the correct answer to the question of how fraternal twins are produced is that two ova are fertilized simultaneously by two sperm.

**Final Answer**: Option D: Two ova are fertilized simultaneously.

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