Molecular Basis for Relationship between Genotype and Phenotype DNA RNA protein genotype function organism phenotype DNA sequence amino acid sequence transcription translation

wild-type CAU CAU CAU CAU CAU HIS HIS HIS HIS HIS Frameshift Mutations and Suppressor Mutations frameshift mutations: insertions or deletions of nucleotides that cause a shift in the translational reading frame suppressor mutations: mutations that counteract or suppress the effects of another mutation CAU ACA UCA UCA UCA U __ HIS THR SER SER SER. addition of A CAU ACU CAU CAU CAU HIS THR HIS HIS HIS deletion of A CAU CAC AUC AUC AU __ HIS HIS ILE ILE. deletion of U CAU CAC GAU CAU CAU HIS HIS ASP HIS HIS addition of G

Gene (Point) Mutation: One allele changes to a different allele. Effects are limited to that locus. Chromosome Mutation: Changes occur at the chromosome level. Multi-locus effects are not unusual. Mutation: Levels of Hereditary Change

Molecular Basis for Relationship between Genotype and Phenotype DNA RNA protein genotype function organism phenotype DNA sequence amino acid sequence transcription translation

Base substitution: change in base of nucelotide pair Base additions: insertion of nucleotide pairs Base deletions: deletion of nucleotide pairs Point mutations at the molecular level

Consequences of Point Mutations within Genes

Point Mutations Can Alter mRNA Splicing

Point Mutations on Gene Products

Mutagens are agents that cause mutations. Anything that is capable of causing chemical changes in the structure of DNA (especially bases) is a mutagen. Mutagens differ in mutagenicity. Mutation frequencies obtained with various mutagens in Neurospora

The Ames Test Reveals Mutagenic Compounds Strain 1 - frameshift mutation Strain 2 - base substitution

Revertant colonies per culture plate. Ames Test Results 1 1 McCann et al., Proc. Natl. Acad. Sci. USA Treatment Control diethyl sulfate* ICR-191** TA TA , TA1575 : his base substitution mutant TA1578 : his frameshift mutant * Highly toxic alkylating agent, occurs as colorless liquid with peppermint odor ** Acridine, colorless solid intercalating agent, known carcinogen