This document summarizes key aspects of mammalian cleavage. It begins by defining cleavage as the rapid cell divisions that occur after fertilization. It then describes different patterns of mammalian cleavage based on cleavage furrows, fate of germ layers, and cell arrangement. The importance of cleavage in generating cells for differentiation and increasing the nucleus to cytoplasm ratio is highlighted. Key stages of early embryonic development including fertilization, cleavage, gastrulation and organogenesis are outlined. The document concludes by detailing the specific cell divisions and structures that arise during cleavage and blastula formation in mammals.

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2. CLEAVAGE in
mammals

3. • Cleavage
• Patterns of mammalian cleavage
• Importance of cleavage
• Early embryonic development
• Development step: cleavage and blastula.
CONTENT

4. Cleavage is a rapid series of mitotic
divisions that occur just after
fertilization.The process follows
fertilization, with the transfer being
triggered by the activation of a
cyclin-dependent kinase complex.
WHAT IS CLEAVAGE ?

5. Patterns of mammalian cleavage
The repeated cleavage furrows produce a number of
blastomeres which exhibit a specific pattern of
arrangement.
The following types of cleavage patterns are:-
• On the basis of cleavage furrow.
• On the basis of fate of germ layers.
• On the basis of arrangement of the cells.

6. Importance of cleavage
The critical reasons why cleavage is so
important:-
1. Generation of a large number of cells that
undergo differentiation and gastrulation to
organs
2. Increase in the nucleus /cytoplasmic ratio.
3.It converts a unicellular zygote into a
embryo.
4 . It brings about the distribution of cytoplasm
among the blastomere.

7. Mammalian
CLEAVAGE

8. Early embryonic development
four essential stages in early embryonic development:
1. Fertilization: the process of a single sperm cell combining with single egg
cell to form a zygote.
2. Cleavage: the first major phase of embryonic development,it gives rise to
blastomere.
3. Gastrulation: the dramatic rearrangement of cells in the blastula to create
the embryonic tissue layers.
4. Organogenesis: the process of organ and tissue formation via cell division
and differentiation.

10. Development step:cleavage and
blastula
• The mammalian oocyte is released from the ovary. Fertilization
occurs in the ampulla of the oviduct.
• Meiosis is completed at this time, and first cleavage begins
about 30 hours after fertilisation.
• The cilia in the oviduct push the embryo toward the uterus; the
first cleavages occur along this journey.

11. The first cleavage

12. • the second cleavage, one of the two blastomeres divides
meridionally and the other divides equatorially. This type of
cleavage is called rotational cleavage.
• In the third cleavage most other embryos is the marked
asynchrony of early cell division.
• In fourth cleavage , genome is activated during early cleavage,
and produces the proteins necessary for cleavage to occur.

14. • The fifth cleavage involves the phenomenon of
compaction,the blastomeres suddenly huddle together,
maximizing their contact with one another and forming a
compact ball of cells.
• The cells of the compacted 8-cell embryo divide to produce a
16-cell morula.The morula consists of a small group of internal
cells surrounded by a larger group of external cells.
• Most of the descendants of the external cells become the
trophoblast (trophectoderm) cells,it forms placenta.

15. • These cells generate the inner cell mass (ICM), which will give rise to
the embryo and its associated yolk sac, allantois, and amnion.
• By the 64-cell stage, the inner cell mass (approximately 13 cells) and
the trophoblast cells have become separate cell layers.
• During a process called cavitation, the trophoblast cells secrete fluid
into the morula to create a blastocoel.
• The inner cell mass is positioned on one side of the ring of
trophoblast cells . The resulting structure, called the blastocyst.
• Centrall located, inner cell mass or embryoblasts gives rise to
embryo.

17. References
• https//:Courses.lumenlearning.com
• https//:britanica.com
• Https//:biologydiscussion.com
• https//:chegg.com

18. THANK YOU