Lecture: Mitosis

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Lecture Mitosis Meiosis Manifestations of
Mendels Laws at the cellular level
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Outlines

• Chromosomes in general
• Mitosis
• Meiosis
• Relevance to Mendels Law
• Meiosis versus Segregation Law
• Meiosis in humans

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Chromosome in general (history)

• chromosomes means colored bodies
• (DNA proteins)
• Chromosomes were discovered around the Mendels
  time.
• Nucleic acids 1868
• Chromosomes 1888
• Discovery of meiosis 1890
• Chromosome theory for Mendels Laws 1902
• Double-helix structure of DNA 1953
• Sequencing entire human chromosomes 2000

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Chromosome in general (size, shape and number)

• Two sister chromatids per chromosome
• DNA replication ---gt chromatids
• Two sister chromatids joined together
• at centromeres
• chromosomes differ in size and appearance with
  staining

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Chromosome in general (size, shape and number)

• Diploid organisms 2n
• Two copies of autosomes
• with sex chromosomes
• diploid organisms have two cell-types
• somatic cells bodys cells
• germ cells gametes
• human bodies 1014 cells
• many cell divisions gt mitosis
• sexual reproduction
• require haploid (n) cells gt meiosis

Human chromosomes 22 pairs of autosomes sex
chromosome (XX or XY)
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Mitosis

• Chromosome duplication as part of cell division
• Growth and development
• wounds healing and cell replacement
• two daughter cells with identical sets of
  chromosomes as parent cells
• Prophase-metaphase-anaphase-telophase
• Note the key difference btw mitosis vs meiosis

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Mitosis
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Meiosis

• Reducing chromosome numbers in half for gamete
  cells (2n gt n)
• One duplication followed by two
• consecutive cell divisions
• 2n --------gt n
• two divisions meiosis I meiosis II
• meiosis I two homologs split into two
• synapse and crossing-over
• meiosis II two sister chromatids split into two

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Meiosis (vs Mitosis)

• Separation of two homologs
• (only in meiosis)
• vs
• Separation of two sister chromatids
• (both in mitosis and meiosis)

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Relevance to Mendels Law

• Segregation law
• separation of two homologs
• Independent assortment law
• assorting different combinations of
  multiple genes alleles

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Meiosis in human (male)

• Produces gametes continuously from puberty ---gt
  forever meiosis!

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Meiosis in human (female)

• Produces 1x106 primary oocytes at 3 month
  gestation period. These cells are arrested
  prophase I until ovulation (12-40 years later)
• One oocyte goes through one complete meiosis each
  month to produce one final egg (not 4 eggs)

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Summary of mitosis and meiosis
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Homework for nextweek
4-1, 4-2, 4-3, 4-6, 4-7, 4-8, 4-10, 4-16