Cytogenetics: Chromosome Mutations, Aberrations & Evolution

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Cytogenetics Chromosome Mutations, Aberrations
Evolution
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Chromosomes
Prokaryote Eukaryote
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Eukaryotic chromosomes
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Human karyotype
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Why do we care?

• Many diseases and birth defects are a direct
  result of missing, broken, or extra chromosomes.
• Down Syndrome
• Cri du chat Syndrome
• Patau Syndrome

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Mutations at the level of the homologous pair

• EUPLOIDY "true" ploidy, meaning two members of
  each homologous pair.
• ANEUPLOIDY "not true" ploidy, meaning more or
  fewer members than two of each homologous pair.
• MONOSOMY - one homolog partner is missing
• TRISOMY - three homologs
• NULLISOMY- one entire homologous pair is missing.

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Monosomy and Trisomy
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Down Syndrome
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How does it happen? Nondisjunction
Each chrom. has two chromatids
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Trisomy Patau Syndrome

• 1/20,000 births
• severe mental retardation
• heart and organ defects
• polydactyly
• death by the age of one year

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Structural Changes

• Deletions (deficiencies)
• Duplications
• Inversions
• Translocations

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Deletions (deficiencies)
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How can chromosomes break?

• Ionizing radiation (production of free radicals,
  which act like little atomic "cannon balls",
  blasting through strands of DNA or c'somes.
• Chemical insult.

Why do they rejoin?
Break points of chromosomes are highly reactive
("sticky"), whereas normal ends of c'somes are
capped by telomeres, which do not readily bond to
other molecules.
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• Breaks that occur ______ __________________
  __________________ will affect both newly formed
  chromatids, all daughter cells arising from
  them.
• Breaks that occur ______ ____________________
  ____________________ may affect only one
  chromatid. (Thereafter, only the progeny carrying
  the broken chromatid will be affected.)

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Cri-du-chat Syndrome

• _________________
• _________________
• Mental retardation
• Slow motor skill development
• Low birth weight and slow growth
• Small head (microcephaly)
• Partial webbing of fingers or toes
• Wide-set eyes (hypertelorism)
• High-pitched cry

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Structural Changes

• Deletions (deficiencies)
• Duplications
• Inversions
• Translocations

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Duplication
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Duplications
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Bar eye caused by duplication
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Duplications source of evolutionary novelty?
Duplication is a source of new genes over
evolutionary time e.g., gene families like
globins and MHC genes

• ______________
• ______________
• ______________
• ______________

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Structural Changes

• Deletions (deficiencies)
• Duplications
• Inversions
• Translocations

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Inversions
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