Key Concept Mutations are changes in DNA that may or may not affect phenotype. mutated base
What Are Mutations? Changes in the nucleotide sequence of DNA May occur in somatic cells (aren’t passed to offspring) May occur in gametes (eggs & sperm) and be passed to offspring
Are Mutations Helpful or Harmful? Mutations happen regularly Almost all mutations are neutral Chemicals & UV radiation cause mutations Mutagens are anything in the environment that can cause mutations Many mutations are repaired by enzymes
Are Mutations Helpful or Harmful? Some types of skin cancers and leukemia result from somatic mutations Some mutations may improve an organism’s survival (beneficial)
Silent Mutations Some mutations have no effect and are called “silent” Example: GUC changed to GUG Both code for the amino acid valine This would not affect the protein being made in any way
Mutations may or may not affect phenotype. Chromosomal mutations tend to have a big effect. Some gene mutations change phenotype by: causing a premature stop codon. causing a change in protein shape or the active site. causing a change in gene regulation.
Some gene mutations do not affect phenotype. A mutation may be silent because…. –It occurs in a non-coding region. –It may not affect protein folding or the active site.