Chromosomes From a Cytogenetic Perspective

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• Chromosomes From a Cytogenetic
  Perspective

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Survey lectures!
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Prokaryotic structures (genophores)
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• Eukaryotes
• Have true chromosomal structures.
• Chromosomes undergo mitosis and meiosis.
• Complex interactions between proteins and nucleic
  acids in the chromosomes regulate gene and
  chromosomal function.

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• The nucleus contains most of the cell's DNA,
  allowing for sophisticated regulation of gene
  expression.
• The nuclear envelope is a double membrane that
  surrounds the nucleus.

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• The nucleus contains subcompartments that are
  not membrane-bound.
• The nuclear envelope contains pores used for
  importing proteins into the nucleus and exporting
  RNAs and proteins from the nucleus.

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• A chromosome consists of a single molecule of
  DNA and its associated proteins.
• What is the evidence that a chromosome
  consists of a single piece of DNA?

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1) Harlequin chromosomes
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1) Harlequin chromosomes
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• 2) Pulsed-field gel electrophoresis - separation
  of chromosomes
• 3) Analysis of the complete nucleotide sequence
  of many genomes now
• 4) In situ hybridization (below)

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• The DNA and protein complex found in eukaryotic
  chromosomes is called chromatin
• 1/3 DNA and 2/3 protein

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Heterochromatin vs Euchromatin
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How are chromosomes distinguished?
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Karyotype is the representation of entire
metaphase chromosomes in a cell, arranged in
order of size and other characteristics.
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Morphological characteristics of chromosomes -
Size
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Idiogram
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Specific staining procedures

• G-banding - Giemsa stain
• R-banding - reverse banding
• C-banding
• Q-banding
• Fluorescent banding

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Chromosome Painting
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Fluorescent Labeling of Chromosomes
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• What structures are necessary to a functional
  eukaryotic chromosome?
• Centromeres
• Telomeres
• Origins of replication

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Centromeres

• Heterochromatin
• Kinetochore - spindle fiber attachment
• No universal DNA sequences
• Repeat sequences - CENs - 5 to 170 bp humans,
  alphoid satellite repeats
• Specific associated proteins

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Telomeres
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Telomeres

• About 15,000 bp in humans
• Lagging strand problem
• Telomere shortening
• Hayflick and then we die
• Cancer, AIDs, stem cells

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Origins of Replication
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• The structure and organization of chromosomes
  change during the course of the cell cycle.

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Nonrandom chromosome positioning

• Gene rich chromosomes toward center
• Gene poor chromosomes toward periphery
• Centromeres are not the determining factor
• Chromosomes with adjacent positions more likely
  to interact cytolologically

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How porous are territories?

• Previously it was predicted that active genes
  would be located at the surface of chromosome
  territories.
• Now, it appears that they are also in the
  interior
• Some are also found on loops outside of the
  territory

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