Explain the process of early cleavage till the formation of morula.

Explanation

Cleavage is a process of rapid mitotic division of zygote to form a hollow spherical multi-cellular development stage called blastula.
2. After fertilization the zygote undergoes repeated division.
3. Cleavage occurs during its passage through the fallopian tube to the uterus.
5. In human beings, Clevage is holoblastic and equal.
6. As division are rapid, cells become daughter cells are called blastomers.
7. Cleavage shows faster synthesis of DNA
8. The size of morula is equal to fertilized ovum as Zona pellucida remains intact during cleaves.
First cleavage:
1. First cleavage is vertical and its takes place along the animal pole-vegetal pole. 2. Zygote is dividend into two blastomeres
3. It takes place about thirty hours after fertilization
Second cleavage:
1. Second cleavage is also vertical but at right angles to the first one.
2. It divides both blastomeres resulting in four celled stage.
` 3. It occurs within sixty hours after horizontal fertilization
Third cleavage:
1. Third cleavage is a horizontal or latitudinal division and at right angles to the first two cleavage
2. It divides all four blastomeres horizontal forming an eight-called stage.
3. It takes place about seventy-two hours after fertilization
Morula:
1 . Further division produce a solid ball of cells called morula (little mulberry )
2. It consists of 16 cells
3. There are two types of cells (outer layer of smaller clearer cells and an linner mass of larger cells)
4. Morula reaches the uterus about 4-6 days after fertilization.
5.The function of zona pellcucida is to prevent the implantation of the blastocyst at an abnormal site.
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