Division of zygote took place on 5th day after fertilization. What is the type of twinning:
**Core Concept**
The question is testing the understanding of twinning in the context of embryonic development. Specifically, it is asking about the type of twinning that occurs when the division of the zygote takes place after the first few cell divisions. This concept is crucial in embryology, as it helps in understanding the development and characteristics of monozygotic twins.
**Why the Correct Answer is Right**
When the division of the zygote takes place on the 5th day after fertilization, it is considered as a late split or a delayed division. This type of division leads to the formation of monochorionic-diamniotic (MoDi) twins, where the twins share the same placenta but have separate amniotic sacs. The delayed division results in the formation of two separate embryoblasts and two separate trophoblasts, which eventually give rise to the two separate fetuses.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the division of the zygote on the 5th day after fertilization does not lead to the formation of monochorionic-monoamniotic (MoMo) twins, where the twins share both the placenta and the amniotic sac.
* **Option B:** This option is incorrect because the division of the zygote on the 5th day after fertilization does not lead to the formation of dichorionic-diamniotic (DiDi) twins, where the twins have separate placentas and amniotic sacs.
* **Option D:** This option is incorrect because the division of the zygote on the 5th day after fertilization does not lead to the formation of conjoined twins, which are a type of monozygotic twin that shares a body part.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the timing of the division of the zygote determines the type of twinning. Late splits, like the one described in the question, typically result in MoDi twins, whereas early splits result in DiDi twins.
**Correct Answer: C. Monochorionic-diamniotic (MoDi) twins**