CLEAVAGE TYPES holoblastic,meroblastic.

1. CELL CYCLE PHASES
•G1 IS FIRST GROWTH PHASE. CELL
GROWS TO MAXIMUM SIZE BEFORE
DIVISION.
•S IS DNA SYNTHESIS PHASE.DNA
DOUBLES IN THIS PHASE.
•G2 IS SECOND GROWTH PHASE.

2. CLEAVAGE
•REPEATED MITOTIC DIVISION OF THE
ZYGOTE TO FORM MORULA
(BLASTULA)IS CLEAVAGE.
•THE MAIN PURPOSE IS FORMATION OF
MULTICELLULAR EMBRYO FROM
SINGLE CELL EGG.

4. CLEAVAGE MITOSIS
•CLEAVAGE MITOSIS IS DIFFERENT FROM
NORMAL MITOSIS.
•IN NORMAL MITOSIS G1,S AND G2 TAKES
PLACE.
•BUT IN CLEAVAGE MITOSIS G1 IS ABSENT.
•S PHASE IS RAPID.

6. CLEAVAGE TYPES
• CLEAVAGE TWO TYPES DEPENDING UPON PLANE OF
DIVISION.
• HOLOBLASTIC AND MEROBLASTIC.
• HOLOBLASTIC :- CLEAVAGE IN WHICH DIVISION PLANE IS
COMPLETE.
• MEROBLASTIC :- CLEAVAGE IN WHICH DIVISION PLANE IS
INCOMPLETE.

7. HOLOBLASTIC CLEAVAGE TYPES
•HOLOBLASTIC IS OF TWO TYPES SUCH
AS
•HOLOBLASTIC EQUAL-CELL DIVIDED
INTO TWO EQUAL AND COMPLETE
CELLS.
•HOLOBLASTIC UNEQUAL-CELLS FORMED

8. MEROBLASTIC CLEAVAGE TYPES
•MEROBLASTIC CLEAVAGE TWO TYPES SUCH
AS
•MEROBLASTIC DISCOIDAL :- CELLS FORMED
AT ANIMAL POLE AS A DISC.
•FOUND IN BIRD.
• MEROBLASTIC SUPERFICIAL :- CELLS
FORMED AT PERIPHERAL PART.

9. N/C RATIO
• CLEAVAGE STOP AFTER THE NUCLEI CYTOPLASMIC RATIO BECOMES EQUAL TO
BODY CELL.
• IT IS LOW IN ZYGOTE AND HIGH IN BLASTULA.