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

Base substitution: change in base of nucelotide pair Point mutations at the molecular level 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

Mutation frequencies obtained with various mutagens in Neurospora 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.

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

Revertant colonies per culture plate. Ames Test Results1 Revertant colonies per culture plate. Treatment Control diethyl sulfate* ICR-191** TA1575 11 14,700 13 TA1578 25 450 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 1 McCann et al., 1975. Proc. Natl. Acad. Sci. USA 72 979-983.