Wednesday, 1/16/13

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• Wednesday, 1/16/13
• Turn in your HW (the article)
• Answer the following in your notes
• Remember
• Why do cells undergo mitosis?
• What is the end result of a cell undergoing
  mitosis?
• Think
• We have discussed how somatic cells (body cells
  other than the gametes egg/sperm) are
  formedwhat process forms the sex cells (the
  gametes-sperm/egg)?

This process is called MEIOSIS.
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The Basics

• Genes (code for things like eye color, skin
  pigmentation, hormones, etc) are located on the
  chromosomes.
• Each organism must inherit one copy of every gene
  from both parents.
• Most organisms have 2 complete sets of genes.
• Those two sets must be separated in Meiosis so
  that each gamete produced contains just one set
  of genes.

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Chromosome

• Humans have 46 total chromosomes.
• 23 came from your mother
• 23 came from your father
• Each pair of chromosomes are referred to as
  homologous chromosomes (What did the root word
  homo mean again?
• All 46 chromosomes are present in every human
  body cell (a.k.a. somatic cell).
• This is the diploid chromosome number (2 sets ).
  (What did the root word di mean again?)

23 pairs
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Gametes

• Gametes are sex cells sperm or egg.
• Gametes contain only 1 copy of each chromosome.
• These cells are haploid (1 set)
• sounds like half, so they only have half of the
  number of chromosomes
• Humans have 23 chromosomes in every gamete. ?Not
  23 pairs, just 23!

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Diploid Haploid

• Diploid a cell with two sets of chromosomes, 2n
• Haploid a cell with one set of chromosomes,
  gametes, 1n or n
• n number of chromosomes in the organism (23 in
  humans)

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Purpose of Meiosis

• Meiosis forms the gametes (sperm and eggs) that
  are necessary for sexual reproduction.
• Gametes need to be haploid so that when they meet
  for fertilization, the zygote (fertilized egg)
  has 2 copies of the genetic material (diploid)
• Meiosis has 2 stages
• Meiosis I Separation of homologous chromosomes
  (different than mitosis)
• Meiosis II Separation of sister chromatids
  (almost identical to mitosis)

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MEIOSIS I

• Main event
• Separation of homologous pairs of chromosomes
• What do you notice about the names of the stages?
• What do you notice about the movements of the
  genetic material during the stages?
• Homologous Pairs Sets of same chromosome from
  different parents

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1. Prophase I

• DNA coils into chromosomes
• Nuclear envelope nucleolus break down
• Synapsis homologous chromosomes pair up into
  tetrads (What does the prefix tetra mean?
  Think tetrahedron)
• Crossing-over homologous pairs switch pieces of
  their chromatids
• Genetic Recombination maternal paternal
  genetic info get shuffled during crossing-over

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Tetrad
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2. Metaphase I

• Tetrads line up in the middle of the cell
• Remember Metaphase middle
• Spindle fibers attach at the centromeres of each
  homologous chromosome (each chromosome in the
  tetrad will have one attached)

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3. Anaphase I

• Each homologous chromosome moves to the opposite
  end of the cell (one member of the pair)
• Independent Assortment random separation of
  chromosomes, allows for genetic variation
• All of the chromosomes from Mom do not go to one
  cell, all from dad into the other they are
  mixed up between the 2 new daughter cells

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4. Telophase I Cytokinesis I

• Two newly formed cells are haploid
• Each chromosome in the new cells is still made up
  of sister chromatids (which contains 2
  identical-ish copies of chromosome not
  necessarily identical because of what process?)

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? MEIOSIS II

• Separation of sister chromatids
• Very similar to how mitosis looks
• Sister Chromatids identical halves of a
  chromosome that has been duplicated

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5. Prophase II

• 2 newly created cells from Meiosis I start to
  divide

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6. Metaphase II

• Chromosomes line up in the middle

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7. Anaphase II

• Chromatids separate

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8. Telophase II Cytokinesis II

• 4 new cells, each with half the number of
  chromosomes of the original cell

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Lets Review

1. What are gametes?
2. Are gametes produced through mitosis or meiosis?
3. What is separated during meiosis II?
4. What is separated during meiosis I?
5. What is one way that genetic diversity of
   daughter cells is increased during meiosis?
   (think about it, we covered 2 ways in lecture)

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Agenda for today

• Finish notes (3 or less slides)
• Using available resources, complete worksheet.
  If you are seen not working, points will be
  deducted.
• Due tomorrow at the beginning of class. Will be
  looking at CONTENT, not COMPLETION

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Development of Gametes

• Spermatogenesis production of sperm cells
• Oogenesis production of mature egg cells

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Nondisjunction

• Nondisjunction failure of homologous pairs to
  separate in Meiosis I
• If an organism survives, it may have a genetic
  disorder

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Polyploidy

• Polyploid organisms with more than the usual
  number of chromosome sets
• Occurs frequently in plants, results in plants
  that are larger than normal

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• http//cellsalive.com/meiosis.htm

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Mitosis vs. Meiosis

• Mitosis
• Body cells
• 2 cells produced
• Diploid (2 of each chromosome)
• Genetically identical to each other AND to the
  original cell

• Meiosis
• Sex cells (sperm/egg)
• 4 cells produced
• Haploid (1 of each chromosome)
• Genetically different