cytogenetics chromosome mutations aberrations evolution
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Cytogenetics: Chromosome Mutations, Aberrations & Evolution

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Cytogenetics: Chromosome Mutations, Aberrations & Evolution. Chromosomes. Prokaryote Eukaryote. Eukaryotic chromosomes. Human karyotype. 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

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chromosomes
Chromosomes

Prokaryote Eukaryote

why do we care
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
mutations at the level of the homologous pair
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.
how does it happen nondisjunction
How does it happen? Nondisjunction

Each chrom.

has two

chromatids

trisomy patau syndrome
Trisomy: Patau Syndrome
  • 1/20,000 births
  • severe mental retardation
  • heart and organ defects
  • polydactyly
  • death by the age of one year
structural changes
Structural Changes
  • Deletions (deficiencies)
  • Duplications
  • Inversions
  • Translocations
how can chromosomes break
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.

slide21
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.)
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

Cri-du-chat Syndrome
structural changes1
Structural Changes
  • Deletions (deficiencies)
  • Duplications
  • Inversions
  • Translocations
duplications source of evolutionary novelty
______________

______________

______________

______________

Duplications: source of evolutionary novelty?

Duplication is a source of new genes over evolutionary time: e.g., gene families like globins and MHC genes

structural changes2
Structural Changes
  • Deletions (deficiencies)
  • Duplications
  • Inversions
  • Translocations
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