Correct sequence in development is :

Options

A. Fertilization `rarr` Zygote `rarr` Cleavage `rarr` Morula `rarr` Blastula `rarr` Gastrula
B. Fertilization `rarr` Zygote `rarr` Blastula `rarr` Morula `rarr` Cleavage `rarr` Gastula
C. Fertilization `rarr` Cleavage `rarr` Zygote `rarr` Blastula `rarr` Gastrula.
D. Cleavage `rarr` Zygote `rarr` Fertilization `rarr` Morula `rarr` Blastula `rarr` Gastrula.

Answer

**Step-by-Step Solution:**

1. **Fertilization**: The process begins with fertilization, where the male gamete (sperm) and female gamete (egg) unite to form a zygote.

2. **Zygote Formation**: After fertilization, the zygote is formed. This is a single-cell structure that contains genetic material from both parents.

3. **Cleavage**: The zygote undergoes a series of rapid cell divisions known as cleavage. This process does not increase the overall size of the embryo but divides the zygote into smaller cells.

4. **Morula Formation**: After several rounds of cleavage, the zygote develops into a solid ball of cells known as the morula, which typically consists of about 16 cells.

5. **Blastula Formation**: The morula continues to divide and eventually forms a hollow structure called the blastula. The blastula has an outer layer of cells (blastoderm) and an inner cavity (blastocele).

6. **Gastrula Formation**: The blastula undergoes further differentiation to form the gastrula, which has distinct layers of cells. This process is known as gastrulation, and the gastrula can be either diploblastic (two layers) or triploblastic (three layers).

**Correct Sequence**: Fertilization → Zygote → Cleavage → Morula → Blastula → Gastrula

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