CLEVAGE of Fertilization and the part EG

Thins is about cleavage

1. VAna 101 - Veterinary Developmental Anatomy (EMBRYOLOGY) EMMANUEL B. LASAFIN , DVM - 2B Aklan State University CLEAVAGE (THE SEGMENTATION PROCESS)

2. Cleavage is the process of rapid cell division that occurs in the early stages of embryonic development after fertilization. During cleavage, the zygote (fertilized egg) undergoes multiple mitotic divisions without significant growth, resulting in a cluster of smaller cells called blastomeres. CLEAVAGE

3. CLEAVAGE Cleavage, a series of mitotic divisions whereby the enormous volume of egg cytoplasm is divided into numerous smaller, nucleated cells. The division of a fertilized egg into multiple cells, marking the beginning of embryonic development. In most species the rate of cell division and the placement of the blastomeres with respect to one another is completely under the control of the proteins and mRNAs stored in the oocyte by the mother.

4. Cleavage is the initial series of mitotic cell divisions that occur in a zygote (fertilized egg) after fertilization. It transforms the zygote into a multicellular structure called a blastula. The resulting cells, called blastomeres, are smaller than the original zygote. Cleavage does not involve growth; the total mass of the embryo remains the same. CLEAVAGE

5. STAGES OF CLEAVAGE

6. - Cleavage stage in most animals during embryonic development: 1. Early cleavage stages • 2-cell stage • 4-cell stage • 8-cell stage 2. Morula 3. Early blastula 4. Late blastula CLEAVAGE STAGES

7. EARLY STAGES OF CLEAVAGE 2-cell stage: The zygote divides into two blastomeres. 4-cell stage: Each blastomere divides, resulting in four blastomeres. 8-cell stage: Further division leads to eight blastomeres.

8. THE MORULA STAGE

9. An embryo at an early stage of embryonic development, consisting of cells (blastomeres) in a solid ball contained within the zona pellucida. 0.1-0.2 mm 1.5-3 days post ovulation - Blastomeres change their shape and tightly align themselves against each other to form a compact ball of cells MORULA STAGE

10. THE BLASTULA STAGE

11. BLASTULA STAGE It is produced by cleavage of a fertilized ovum. Consists of a spherical layer of around 128 cells with a large fluid filled space called the blastocoel in the animal pole of the embryo. An embryo which has developed to the point of having 2 different cell components and a fluid cavity (blastocoel) 0.1-0.2 mm 4 days post-ovulation

12. THE TYPES OF CLEAVAGE

13. EFFECT OF THE DIFFERENT TYPE OF YOLK ON CLEAVAGE

14. EFFECT OF THE DIFFERENT TYPE OF YOLK ON CLEAVAGE Yolk is needed for embryonic development. However, the fertilized egg has to undergo all stages of development and result in a suitable ‘young form’ initiating next generation. Somehow with all the influences of yolk the developmental procedures are so adapted and modified that a well-formed embryo will result. The initial influence of yolk is felt during the process of cleavage. The amount of the yolk and its distribution affect the process of cleavage.

15. EFFECT OF THE DIFFERENT TYPE OF YOLK ON CLEAVAGE 1. Solecithal eggs (iso = equal) • Have a small amount of yolk that is equally distributed in the cytoplasm (most mammals have isolecithal eggs). • Amounts of yolk distributed throughout the cytoplasm of the egg 2. Mesolecithal eggs (meso = middle) • Have a moderate amount of yolk, and the yolk is present mainly in the vegetal hemisphere (amphibians have mesolecithal eggs). • Amount of yolk distributed throughout the cytoplasm (toward the vegetal pole)

16. EFFECT OF THE DIFFERENT TYPE OF YOLK ON CLEAVAGE 3. Telolecithal eggs (telo = end) • Have a large amount of yolk that fills thecytoplasm, except for a small area near the animal pole (ex. fish, reptiles, and birds). • Amounts of yolk concentrated at one end of the egg (ex. chicken) 4. Centrolecithal eggs • have a lot of yolk that is concentrated within the center of the cell (insects and arthropods).

17. No growth period Blastomere does not increase in size before the next division begins At the end of cleavage, the cells are usually smaller than most of the differentiated cells of an adult animal Nuclei of the early cleavage cells are larger than they are in ordinary somatic cells of the same animal OVERALL CHARACTERISTICS OF A CLEAVAGE

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