Cleavage in detail.........
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Explanation:
cleavage:In mearals,cleavage is evident when crystals split along planes of weakness inherent in the structure of their atomic.
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Meaning of Cleavage:
Fertilization results into the formation of zygote. The process of segmentation (cleavage) immediately follows fertilization or any other process which activates the egg. Cleavage consists of division of the zygote into a large number of cellular entities. The cells which are produced during segmentation are called blastomeres.
At first, the cells remain closely associated, but later on they form the lining of a hollow sphere called blastula. The blastula contains a cavity named blastocoel and its outer covering is designated as blastoderm. The formation of blastula culminates the cleavage period.
Planes of Cleavage:
During early cleavage, distinct geometrical relationships exist between the blastomeres, i.e., each plane of cell-division bears a definite relationship with each other.
a. Meridional plane of cleavage:
When a furrow bisect both the poles of the egg passing through the median axis or centre of egg it is called meridional plane of cleavage. The median axis runs between the centre of animal pole and vegetal pole.
b. Vertical plane of cleavage:
When a furrow passes in any direction (does not pass through the median axis) from the animal pole towards the opposite pole.
c. Equatorial plane of cleavage:
This type of cleavage plane divides the egg halfway between the animal and vegetal poles and the line of division runs at right angle to the median axis.
d. Latitudinal plane of cleavage:
This is almost similar to the equatorial plane of cleavage, but the furrow runs through the cytoplasm on either side of the equatorial plane.
3. Types of Cleavage:
Considerable amount of reorganisation occurs during the period of cleavage and the types of cleavage depend largely upon the cytoplasmic contents.
Different types of cleavage encountered in different eggs are catalogued below:
a. Holoblastic op total cleavage:
When the cleavage furrows divide the entire egg.
It may be:
Equal:
When the cleavage furrow cuts the egg into two equal cells. It may be radially symmetrical, bilaterally, symmetrical, spirally symmetrical or irregular.
Unequal:
When the resultant blastomeres become unequal ir size
Hope it helps!!
Fertilization results into the formation of zygote. The process of segmentation (cleavage) immediately follows fertilization or any other process which activates the egg. Cleavage consists of division of the zygote into a large number of cellular entities. The cells which are produced during segmentation are called blastomeres.
At first, the cells remain closely associated, but later on they form the lining of a hollow sphere called blastula. The blastula contains a cavity named blastocoel and its outer covering is designated as blastoderm. The formation of blastula culminates the cleavage period.
Planes of Cleavage:
During early cleavage, distinct geometrical relationships exist between the blastomeres, i.e., each plane of cell-division bears a definite relationship with each other.
a. Meridional plane of cleavage:
When a furrow bisect both the poles of the egg passing through the median axis or centre of egg it is called meridional plane of cleavage. The median axis runs between the centre of animal pole and vegetal pole.
b. Vertical plane of cleavage:
When a furrow passes in any direction (does not pass through the median axis) from the animal pole towards the opposite pole.
c. Equatorial plane of cleavage:
This type of cleavage plane divides the egg halfway between the animal and vegetal poles and the line of division runs at right angle to the median axis.
d. Latitudinal plane of cleavage:
This is almost similar to the equatorial plane of cleavage, but the furrow runs through the cytoplasm on either side of the equatorial plane.
3. Types of Cleavage:
Considerable amount of reorganisation occurs during the period of cleavage and the types of cleavage depend largely upon the cytoplasmic contents.
Different types of cleavage encountered in different eggs are catalogued below:
a. Holoblastic op total cleavage:
When the cleavage furrows divide the entire egg.
It may be:
Equal:
When the cleavage furrow cuts the egg into two equal cells. It may be radially symmetrical, bilaterally, symmetrical, spirally symmetrical or irregular.
Unequal:
When the resultant blastomeres become unequal ir size
Hope it helps!!
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