Unit 2; Continuity of Life; Cell Cycle & Cell Division
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- Created on: 08-11-16 14:52
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- Cell Cycle & Cell Division
- Cells & Chromosomes
- Chromosomes are DNA and histone protein, visible when chromatin condenses
- Haploid number: # of chromosomes in full set
- Homologous Pairs: matching pairs of chromosomes
- Ploidy Level: number of full sets in an organism, Humans are diploid
- Mitosis
- 2 identical daughter cells produced
- 1. Interphase
- long with high metabolic activity
- new cells grows & organelles replicate
- replication of DNA occurs
- Histones & enzymes synthesised
- 2. Prophase
- chromosomes coil, shorten, thicken
- centrioles in animals cells separate and go to opposite ends
- protein microtubules form spindle between centrioles
- nuclear envelope and nucleolus disappear
- 3.Metaphase
- chromosomes attach to spindle at centromere
- align along equator
- 4. Anaphase
- Centromere separates
- Spindle contracts with protein microtubules
- Chromatids pulled to poles, centromere first
- 5. Telophase
- chromosomes uncoil & lengthen
- spindle breaks down
- nuclear envelope & nucleolus reappear
- 6.Cytokineses
- cytoplasm divides to 2 cells
- In plants; cell plate forms across equator for new wall
- Significance of Mitosis
- Maintans chromosome number for genetic stability
- Growth: tissue repair and dead cell replacement
- Asexual Reproduction in unicellular organisms
- Damage and Disease
- if genes controlling cycle are damaged
- if cells divide too frequently, tumours are formed
- cells wont divide causing problems for growth etc
- if cells divide too frequently, tumours are formed
- cells wont divide causing problems for growth etc
- if genes controlling cycle are damaged
- Meiosis
- 4 genetically dif daughter cells
- Occurs in reproductive organisms before sexual reproduction
- Diploid halved to haploid so becomes diploid again in reproduc-
- Meiosis I
- Prophase I
- homologous pairs come together (as bivalent) CROSS OVER each other
- repel but remain joined at chiasmata where DNA segments are exchanged; genetic variation
- Chromosome condense & centrioles separate
- Metaphase I
- bivalents attach to spindle and align on equator
- lie randomly with either pair facing either pole; genetic variation
- Anaphase i
- bivalents separate & go to opposite poles as spindle contracts
- Each pole has maternal & paternal c-somes due to independent assortment
- Telophase I
- nuclear envelope reforms
- Prophase I
- Meiosis II
- Prophase II
- centrioles separate and organise new spindle at 90* to old one
- Metaphase II
- Chromosomes line on equator
- independent assortment occurs; genetic variation
- Anaphase II
- centromeres divide and spindle shortens, pulling chromatids to opposite poles
- Telophase II
- chromatids lengthen
- spindle disintergrates
- nuclear envelope and nucleolus reappear
- Cytokinesis occurs at end, same as in Mitosis
- Prophase II
- Differences between Mitosis and Meiosis
- Daughter cells produced
- Mitosis: 2 identical daughter cells
- Meiosis: 4 genetically different
- Number of divisions
- Mitosis has only 1
- Meiosis has 2
- Type of cells it occurs in
- Mitosis: all cells
- Meiosis: only in sex cells
- Crossing over
- occurs in meiosis
- doesn't occur in mitosis
- Chromosome number at end
- Mitosis: remains the same
- Meiosis: reduced by half
- Daughter cells produced
- Cells & Chromosomes
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