Which of the following sequences shows the correct order of the events that occur during foetal development?

Options

A. cleavage `to` fertilisation `to` differentiation `to` implantation
B. fertilisation `to` cleavage `to` implantation `to` differentiation
C. cleavage `to` fertilisation `to` implantation `to` differentiation
D. fertilisation `to` cleavage `to` differentiation `to` implantation

Answer

To determine the correct order of events during fetal development, we need to understand the sequence of processes that occur after fertilization. Here is a step-by-step breakdown of the events:

### Step-by-Step Solution:

1. **Fertilization**: This is the first step where the male gamete (sperm) and the female gamete (ovum) fuse to form a diploid zygote. This process marks the beginning of the development of a new organism.

2. **Cleavage**: Following fertilization, the zygote undergoes a series of rapid cell divisions known as cleavage. This process transforms the single-celled zygote into a multicellular structure, initially forming a solid ball of cells called the morula.

3. **Implantation**: After several rounds of cleavage, the morula develops into a blastocyst. The blastocyst then travels to the uterus and implants itself into the endometrial lining. This is crucial for establishing a connection with the mother's blood supply.

4. **Differentiation**: After implantation, the cells of the blastocyst begin to differentiate. This means that the cells start to develop into different types of cells that will form various tissues and organs of the body.

### Conclusion:
The correct order of events during fetal development is:
**Fertilization → Cleavage → Implantation → Differentiation**.

Thus, the correct option is **Option 2**.

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