Question

Correct sequence in development is
(A) Fertilization $\to$ Zygote $\to$ Cleavage $\to$ Morula $\to$ Blastula $\to$ Gastrula
(B) Fertilization $\to$ Zygote $\to$ Blastula $\to$ Morula $\to$ Cleavage $\to$ Gastrula
(C) Fertilization $\to$ Cleavage $\to$ Morula $\to$ Zygote$\to$ Blastula $\to$ Gastrula
(D) Cleavage $\to$ Zygote $\to$ Fertilization $\to$ Morula $\to$ Blastula $\to$ Gastrula

Answer 1

The development of the embryo takes place by the process of the embryogenesis. This embryogenesis follows the set of processes and it starts with the fusion of the male and the female gamete to produce the embryo and result in the complete individual.

Complete Answer:
- Fertilization is the first process in the process of embryogenesis. It takes place by the fusion of the male and the female gamete. The result of the fertilization is the formation of the zygote.
- Zygote is the type of the eukaryotic cell and contains the genome of both the male and the female gametes. It is the fertilized ovum in the female fallopian tube which is the result of the fertilization.
- After the zygote formation, the process of cleavage takes place. It is defined as the process in which the cells of the zygote undergo the cell division.

- The cells that are divided from the parent zygote cells are called the blastomeres. In humans and animals, the cleavage happened in the radial type. This cleavage then follows the stages of the morula, blastula and the gastrula.
- The morula stage is the stage of the zygote which contains sixteen cells of the blastomeres and the zygote appears as the solid ball. Then the repeated cell division causes the single layer of the cells called blastula and which grows into the multi layered cells called gastrula.

Thus, the option (A) is correct.

Note: Morula appears as the solid ball of the cells and the blastula appears as the hollow ball since it contains only the single layer of the cells. These two processes are followed by the gastrula which appears as the cup shaped cells which are multilayered.