12.4 - Mutations

• • Mutations are changes in genetic material
  • A change in the DNA may then affect translation and the resulting proteins produced
• 2 kinds of mutations: gene mutations & chromosomal mutations

  • gene mutation: change in one or a few nucleotides in DNA - called point mutation
  • insertions - add a nucleotide
  • deletion - lose a nucleotide
  • these tend to be more dramatic b/c they affect all the codon after the mutation
  • a deletion or insertion causes a shift of all the codon grouping (Reading framed) and therefore amino acids, and so is called a frameshift mutation
  • all amino acids are changed
• substitution - another kind of point mutation that involves the substitution of only one nit. base

  • it may change only one amino acid
  • it may not affect the protein if the same amino acid is used
  • however, it can be just as dramatic as a frameshift, if the new codon codes for a premature stop, for example
• Chromosome mutation: change in a whole piece of one chromosome or chromosome # and could involve one or several genes, which are large portions of a chromosome - they usually cause a phenotype change because of the large number of genes affected

  • chromosome mutations include:
  • deletion - lose a piece of chromosome
  • insertion - have a piece of chromosome added to another chromosome
  • translocation - swap genes on a chromosome
  • nondisjunction - lose or add a chromosome to a cell
• • Many mutations are not "harmful" because they may be a silent point mutation - the mutation may be in a non-coding portion of the DNA or not affect a large portion of a gene
  • Some mutations create genetic variety which may allow phenotypes with a selection benefit for an organism if it gives an organism an advantage over other organisms in a particular environment - this is the basis of evolutionary change