Mutations Occur when there is an error in DNA replication Def: Change in genetic material Mutagens Physical or chemical agents that cause mutations Ex: high energy radiation (x-ray or UV) Ex. Chemicals (that are similar to DNA but cause incorrect base pairing)
Mutation Any change in the nucleotide sequence of DNA Large or small 2 Main types Base Substitutions (point mutations) Insertions or deletions
Replacement of one base or nucleotide with another
Usually do not change amino acid
Sometimes causes a change in the protein made
When a substitution does not cause a change in the protein expressed by a gene
Remember some codons represent the same amino acid
Example: GAA and GAG both code for Glu
Point MutationA point mutation is a simple change in one base of the gene sequence. This is equivalent to changing one letter in a sentence, such as this example, where we change the 'c' in cat to an 'h': Original: The fat cat ate the wee rat. Point Mutation: The fat hat ate the wee rat.
Insertion or Deletion
Nucleotide is removed or added
mRNA is read as triplet codes
Adding/removing bases changes these three letter codes
Codons downstream from insertion/deletion will be regrouped and probably code for a non-working protein
Result: FRAMESHIFT MUTATION
Shift the “reading” frame of the genetic message
Frameshift mutation Original: The fat cat ate the wee rat. Frame Shift: The fat caa tet hew eer at.
Involve changes in the number or structure of the chromosome
May change location of genes on chromosome
Deletions: loss of part of chromosome
Duplications: produce extra copies of parts of chromosome
Inversions: reverse direction of chromosome
Translocation: when one chromosome breaks off and attaches to another
Mutations NOT always harmful Some alter a protein in a beneficial way that may help species in a specific environment If mutation is present in organisms gametes, it may be passed off to off-spring Mutations are the ULTIMATE source for GENETIC DIVERSITY!!!