Cell Division
- Created by: N1ntendo-Sw1tch
- Created on: 25-02-23 16:02
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- Cell Division
- Mitosis
- used for: growth, repair/ replacement and asexual reproduction
- Stages
- 1. Prophase (prepare)
- - chromatin condense to chromosomes - nuclear envelope disappears - spindle apparatus radiates from centrioles and move toward poles
- 2. Metaphase (middle)
- - in middle of cell (equator) chromosomes line up - the spindle fibres attach to chromosomes - the chromosomes are now maximally condensed
- 3. Anaphase (apart)
- - the centromeres split - spindle contracts and the chromatids are pulled towards the poles of the cell -each chromatid is pulled along by its centromere
- 4. Telophase (two)
- - the chromatids reach the poles - become less condensed (back to chromatin) -two new nuclear envelopes form
- 5. Cytokinesis
- - the cleavage furrow is formed (gap between the two new cytoplasm) - the cytoplasm divides creating the two new cells
- 1. Prophase (prepare)
- One sister chromatid from parent cell passes into each daughter cell. So no change in chromosome number
- division of one cell into two daughter cells
- Meiosis
- Cells that divide by meiosis include: -sperm cells -egg cells -pollen
- occurs in sexual reproduction. creating four haploid cells from one diploid one. includes two cycles of division
- Division cycle 1 stages
- 1. Prophase 1 (crossing over)
- same as mitosis but chromosomes arrange into homologous pairs (bivalents) and exchange segments of DNA at the chiasmata (crossing over) this means the gene combo of a chromosome can be changed. no crossing over between sister chromatids.
- 3. Anaphase 1
- - the spindles contract and chromosomes are pulled to the poles - bivalents split but centromere doesn't
- 4. Telophase 1
- - the cleavage furrow appears and the cell splits by the end of the stage - cells produced by division 1 are haploid - in some organisms the nuclear envelope returns but not in most
- Division Cycle 2 stages
- 1. Prophase 2
- - if formed nuclear envelope breaks - centrioles replicate and spindles grow outward at right angles from the old ones
- 2. Metaphase 2
- chromosomes move to equator - the spindle fibres attach to the chromosomes= random assortment of sister chromatids
- 3. Anaphase 2
- - the centromere splits - sister chromatids of each chromosomes separate and are pulled to opposite poles
- 4. Telophase 2
- - the chromosomes reach opposite poles - cytokinesis occurs - the two cells produced by division one divide to form four haploid daughter cells - nuclear envelopes reappears
- 1. Prophase 2
- 1. Prophase 1 (crossing over)
- what causes genetic variation in daughter cells? crossing over and random assortment
- Mitosis
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