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Cell Cycle

Mitosis & Meiosis

Tonny Nguyen 3B

Start

Cell Cycle Phases

Cell Cycle Phases

In the cell cycle there are series of stages that must be gone through to completely duplicate a cell.

  • G1 - Metabolic changes prepare the cell for division
  • S - DNA synthesis replicates the genetic material - two sister chromatids
  • G2 - Metabolic changes assemble for mitosis + cytokinesis
  • M - Mitosis + cytokinesis

Mitosis

Mitosis

Purpose of Mitosis:

  • Produce two daughter cells in eukarotic cells that...
  • Have same genetic component of parent cell
  • Have same copies of every chromosome

Mitosis - Prophase

  • Occupies over half the time of mitosis

  • Centrosome duplicates to form two daughter centrosomes at each ends of cell
  • Form mitotic spindle from spindle fibres

  • Chromosomes condense into sister chromatids held by the centromere.

Mitosis - Prometaphase

  • Chromosomes led by centromeres migrate to the middle of the cell.

  • Spindle fibres bind to the centromere of each chromosomes as they continue to condense.

Mitosis - Metaphase

  • Chromosomes align along the metaphase plate of the spindle apparatus.

Mitosis - Anaphase

  • Shortest stage of mitosis
  • centromeres divide and chromosomes pull apart

  • Pulled apart chromosomes are now called daughter chromosomes

Mitosis - Telophase

  • Final stage of mitosis
  • Reversal of prophase
  • Nuclear membrane reforms around chromosomes

  • Chromosomes uncoil, diffuse and spindle fibres disappear.

Mitosis - Cytokinesis

  • Final cellular division - forms two new cells
  • Animal - constriction of cytoplasm
  • Plant - cell plate form along line of metaphase plate

Meiosis

Meiosis

Purpose of Meiosis:

  • Produce gametes from diploid cells and create genetic diversity

Meiosis I - Prophase

  • Homologous chromosomes pair + exchange DNA to form recombinant chromosomes
  • Leptotene - condense chromosomes
  • Zygotene - Form pairs of chromosomes of 4 chromatids
  • Pachytene - Crossing over of chromosomes to form chiasmata
  • Diplotene - Chromosomes separate
  • Diakinesis - Chiasmata moves to end of chromosomes

Meiosis I - Metaphase

  • Homologous pairs of chromosomes - arranged as double row along metaphase plate
  • Arrangement is random - similar not identical to parent

Meiosis I - Anaphase

  • Homologous chromosomes are separated and move to opposite poles of the cell

Meiosis I - Telophase

  • Chromosomes become diffuse and nuclear membrane reforms.

Meiosis I - Cytokinesis

  • Final cellular division to form two new cells - followed by Meiosis II

Meiosis II + Comparison

  • Overall events of Meiosis II are analogous to mitosis. - separate each chromosome into two chromatids - BUT dealing with half the amount of chromosomes
  • Meiosis unlike mitosis - creates GENETIC DIVERSITY
  • exchange of genetic material during Meiosis I
  • random alignment of maternal + paternal chromosomes in Meiosis I
  • random alignment of sister chromatids in Meiosis II
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