Oogenesis
The formation of the ovum (mature female gamete) from undifferentiated germ cells is called oogenesis. This process takes place in the ovaries (female gonads). Oogenesis consists of three stages known as the multiplication phase, growth phase, and maturation phase.
Cell Division
Cell division involves the formation of new daughter cells from the parent cells. It is a part of the cell cycle that takes place in both prokaryotic and eukaryotic organisms. Cell division is required for three main reasons:
What are the variuos stages in the mitotic cell cycle.
The mitotic cell cycle is the process where the parent cell divides into two identical daughter cells. Here the DNA of the parent cell is replicated into two identical copies for the daughter cells. Then the cell divides each having one copy of the parental DNA.
There are five stages of mitotic cell cycle;
1. Interphase: In this stage, the parental DNA is replicated forming two identical sets of chromosomes. The microtubules extend to two centrosomes containing a pair of centrioles that are present outside the nucleus.
2. Prophase: In this stage, the chromosome condenses to form an X-shaped structure. The membrane covering the nucleus breaks away releasing the chromosomes. The mitotic spindle extends across the cell through the centrioles which move towards the opposite poles.
3. Metaphase: In this stage, the chromosome is lined up neatly in the equator of the cell. The mitotic spindle fibers extending from the centrioles present at the opposite poles get attached to the sister chromatids.
4. Anaphase: In this stage, the sister chromatids are pulled towards the poles by the mitotic spindle fibers, one chromatid to each pole.
5. Telophase and cytokinesis: In telophase, the set of full chromosomes gathers at each pole. The chromosomes are covered by a membrane forming the nucleus. Then in cytokinesis, the parent cell is pinched in the middle and two new daughter cells are cut off from the pinched point into two separate cells containing the nucleus bound chromosomes in each cell.
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