Mitosis (and Meiosis)

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Mitosis (and Meiosis)
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Part 1 Cell Division

• Cell division is the cornerstone of life
• Genome a cells complete set of an organisms
  genetic material (DNA)
• Chromosome
• Bacteria, viruses DNA molecule w/ most or all
  DNA
• Eukaryotes DNA / protein structure with part of
  the DNA information

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Chromosomes (colored bodies)

• Prokaryotes have a single, circular chromosome

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Cell Division

• Prokaryotes (bacteria) reproduce through cell
  division
• Binary fission
• Circular chromosome (DNA) is replicated
• Replicated chromosomes are attached to the cell
  membrane at nearby sites
• As membrane expands, the copies separate
• New cell wall forms between copies, cell splits

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Mitosis

• Eukaryotes use cell division to create new cells
• MITOSIS division of the nucleus
• Growth, Maintenance and Repair
• Asexual cell division
• Reproduction
• MEIOSIS a special, two-stage type of mitosis
  that results in daughter cells with half as many
  chromosomes as the parent cells

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Chromosomes

• Eukaryotes have genome distributed across many
  chromosomes
• Humans 46 (23 pairs)
• Mosquito 6 (3 pairs)
• Toad 22 (11 pairs)
• Potato 48 (24 pairs)
• Dog 78 (39 pairs)
• 46 in human somatic cells (all cells EXCEPT
  reproductive cells) 2n
• 23 in gametes (Reproductive cells -sperm and egg)
  n

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Chromosomes (colored bodies)

• Chromosome made of a DNA and protein complex
  chromatin
• Following DNA replication, a chromosome contains
  two sister chromatids attached by a centromere

Chromosome
Sister Chromatids
Centromere
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Humans 46

• 46 chromosomes (2n 46)
• 2 sets of 23 chromosomes (diploid)
• n number of chromosomes in a set
• Fundamental number, haploid number
• n contribution from each parent
• 23 1 sex chromosome, 22 autosomes

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Humans 46

• Maternal Paternal
• Sex
• X or X X or Y
• Autosomes
• 1 1
• 2 2
• 22 22
• (homologous pairs)

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Mitosis and Interphase Alternate

• The cell cycle
• Cells are in interphase 90 of the time
• G1 Gap 1 (cell growth)
• S chromosome synthesis (duplication)
• G2 Gap 2 (cell growth)
• M Mitosis

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Mitosis and Interphase Alternate
The Cell Cycle
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Chromosomes cont.
Homologous pair (2n, diploid) in parent cell
Chromosomes are replicated during S-phase of cell
cycle. Chromosomes and copies are separated
during mitosis.
One of each pair to daughter cell
Copies
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Mitosis is a Contiuum

• But, its divided into subphases for description
• Prophase
• prometaphase
• Metaphase
• Anaphase
• Telophase

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Prophase

• Chromatin coils into visible chromosomes
• Under a light microscope, only the nuclear
  envelope (with nucleoli) and a tangle of
  chromatin are visible
• Centrosomes mitotic centers, poles for division

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prometaphase

• Nuclear envelope breaks
• Microtubules (kinetochore polar) attach
  kinetochores (in centromere) to centrioles (in
  mitotic center aka centrosome)

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Metaphase

• Chromatids align on a plane at cells equator
• Metaphase plate (MITOTIC SPINDLE)

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Anaphase

• Chromatids separate simultanously
• Sister chromatids become daughter chromosomes

Late
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Telophase

• Daughter chromosomes stop moving
• Chromosomes uncoil, nucleus and nucleoli reform
• Result two identical nuclei

Late
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Cytokinesis

• Mitosis nuclear division (karyokinesis)
• Division of cell cytoplasm after mitosis is known
  as cytokinesis

End
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Part 2 Gametogenesis

• Meiosis
• Produces gametes (sperm, egg)
• Gametes are haploid (n)

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Meiosis

• Meiosis is reductionist division
• Highly specialized form of mitosis
• Takes place in gonads
• Produces gametes (sperm and egg)
• Gametes are haploid (n)
• Gametes rejoin during fertilization
• Returns to 2n
• Sexual fertilization results in greater variation

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Chromosome number reduction
Homologous pair of chromosomes in diploid parent
2n 2n n n
CHROMOSOMES REPLICATE
Homologous pair Sister chromatids
Meiosis I Homologues separate into haploid
daughter cells
Meiosis II sister chromatids separate into four
hapliod daughter cells
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Stages of Meiosis

• Meiosis I reduces chromosome number
• Prophase I, Metaphase I, Anaphase I, Telophase I
• Meiosis II separates chromatids
• Prophase II, Metaphase II, Anaphase II, Telophase
  II
• Result four haploid daughter cells

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Stages of Meiosis Meiosis I
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Stages of Meiosis Meiosis II
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Meiosis I

• Prophase I chromatin condenses, homologous pairs
  (with copies) align
• Metaphase I homologous pairs (and copies) align
  at metaphase plate

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Meiosis I

• Anaphase I homologous chromosomes (each with two
  chromatids) move to opposite ends
• Telophase I chromosomes gather into nuclei,
  original cell divides

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Meiosis II

• Interphase with no DNA replication (interkinesis)
  
• Prophase II chromosomes condense again
• Metaphase II kinetochores of paired chromatids
  align at metaphase plate

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Meiosis II

• Anaphase II chromatids separate to opposite
  poles (gt chromosomes)
• Telophase II chromatids gather into nuclei,
  cells divide

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Results

• Gametes are haploid (n) half as many
  chromosomes as parent cell

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Overview

• Meiosis I (2n6)

Metaphase I Homologous pairs (with copies) align
Interphase
Prophase I
Telophase
Anaphase
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Overview

• Meiosis II (result n3)

Metaphase II
Anaphase II
Telophase II
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ENDChapter 9 from Life book