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Molecular Basis for
Relationship between Genotype and Phenotype
genotype
DNA
DNA sequence
transcription
RNA
translation
protein
function
phenotype
organism
amino acid
sequence
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
wild-type
CAU CAU CAU CAU CAU
HIS HIS HIS HIS HIS
addition of A
CAU ACA UCA UCA UCA U__
HIS THR SER SER SER
.
deletion of U
CAU CAC AUC AUC AU__
HIS HIS ILE ILE
.
deletion of A
CAU ACU CAU CAU CAU
HIS THR HIS HIS HIS
addition of G
CAU CAC GAU CAU CAU
HIS HIS ASP HIS HIS
Mutation: Levels of Hereditary Change
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.
Molecular Basis for
Relationship between Genotype and Phenotype
genotype
DNA
DNA sequence
transcription
RNA
translation
protein
function
phenotype
organism
amino acid
sequence
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
Ames Test Results1
Revertant colonies per culture plate.
Treatment
Control
diethyl sulfate*
ICR-191**
TA1575
TA1578
11
25
14,700
0
13
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.