MUTATIONS

• Mutations are heritable changes in genetic information

• Only mutation in the GAMETES can be passed on from generation to generation

• There can be point mutations and chromosomal mutations

Point Mutation

• A gene mutation that involves changes in one or a few nucleotides.

• They occur at a single point in the DNA sequence

• There are three types: Substitutions Insertions Deletions

• The generally occur during replication – any subsequent cell that came from the original cell can be effected

Substitutions

• One base is changed to a different base

• Usually effect no more than one amino acid

• Sometimes have no overall effect (silent mutation)

Insertions and Deletions

• Point mutation in which one base is removed or inserted from the base sequence

• Effects can be dramatic• Because the code is read in groups of 3 (codon), adding

or removing a base would shift every codon that follows the mutation

• These are also called FRAMESHIFT mutations because they shift the “reading frame” of the genetic message

• Can alter a protein so much that its unable to perform its function

Chromosomal Mutations

• Involve a change in number or structure of chromosomes

• Can change the location of genes on chromosomes, and the number of copies of some genes

Mutagens

• A chemical or physical agent in the environment that could cause a mutation. Examples include:

Tobacco smokeX-RaysEnvironmental pollutantsPesticides

• Cells can sometimes repair the damage; but when they can’t, the DNA sequence is permanently altered.

Harmful vs. Helpful Mutations

• Harmful mutations are those that dramatically change protein structure or gene activity

• Can disrupt normal biological activity and cause genetic disorders (like Sickle cell anemia) and cancer

• Helpful mutations help drive evolution• Proteins produced with new or altered

functions can be useful in a changing environment

• Example: insects resisting pesticides