MUTATION

1
MUTATION

• Definition any change in a nucleotide sequence
• Can occur during.. DNA replicationwill be
  passed to all daughter cells Transcriptionw
  ill affect only the batch of protein made from
  that RNA transcript

2
Causes of Mutations

• Random errors during DNA replication or
  transcription
• Mutagens chemicals or other factors which are
  known to cause mutations, such as UV light,
  X-rays, gamma rays, dioxin
• Carcinogens chemicals which have been
  specifically linkd to cancer-causing mutations,
  such as asbestos

3
Effects of Mutations

• Silent if mutation occurs in a gene that
  is not expressed by that cell if mutation
  alters only one copy of the gene, and the other
  copy is still expressed as dominant if mutation
  occurs in non-coding DNA if mutation does not
  alter amino acid sequence of the protein (because
  of wobble)
• Expressed creates an observable change in
  phenotype

4
Types of cells

• Somatic cell Mutations occur in cells OTHER than
  germ cellsMAY affect the individual in which
  they occur, but will probably NOT be passed to
  offspring
• Germ cell Mutations occur in gamete-forming
  cellswill probably NOT affect the individual in
  which the occur, but MAY be passed to offspring
  (if.)

5
Gross chromosomal mutations
6
Point mutations

• Affect one nucleotide only
• Examples substitution ACG CCG
  insertion/deletion (indels) AATTTCGAC
  AATTCGAC AATTTCAGAC Frame shift mutation
  

7
Missense and Nonsense Mutations

• Missense GUG (valine) GCG (alanine) One
  amino acid replaces another
• Nonsense UAC (tyrosine) UAA (stop) codon for an
  amino acid is replaced by a STOP codon
• Which would you expect to have a more severe
  effect?

8
Some Human genetic diseases and the Mutations
that cause them

• Sickle Cell Anemia a single base substitution in
  the gene for the beta chain of hemoglobin which
  results in a glutamic acid residue(position 6)
  being replaced by valine and changes the behavior
  of hemoglobin dramatically
• Cystic Fibrosis Several different deletions in
  CFTR gene
• Downs Syndrome 2 causes Trisomy 21 and
  Translocation

9
Triplet Repeat Diseases

• Huntingtons disease
• Fragile X Syndrome
• Both of these result from amplification of a
  triplet (codon) within a gene