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:
List and describe the phases of mitosis
Mitosis is a type of cell division in which one mother cell divides to produce two new daughter cells that are genetically identical to itself.In mitosis DNA of nucleus of cell is split into the two equal sets of chromosomes.
Phases of mitosis-There are four basic phases: Prophase,metaphase, anaphase, telophase
Prophase:In Prophase, chromatin condenses into discrete chromosomes.Nuclear envelope breaks down and spindles are formed at opposite poles of cell.Mitotic spindle,composed of microtubules and proteins are formed in cytoplasm.
The two pairs of centrioles move away from one another towards opposite end of cell due to lengthening of the microtubules that are formed between them.Polar fibres reaches from each cell pole to the equator of cell.Kinetochores,which are specialized regions in the centromeres of chromosomes attaches to a type of microtubules called kinetochore fibres.The chromosomes begin to migrate towards the centre of cell
Metaphase:
- Nuclear membrane dissappear completely
- Polar fibres continues to extend from the poles to cell's centre
- Chromosomes attach to polar fibres from both sides of centromeres
- Chromosomes align at the metaphase plate at right angles to spindle poles
- Chromosomes are held at metaphase plate by equal forces of polar fibres pushing the centromeres of Chromosomes
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