Mutation

Mutation

1. A change in the nucleotide sequence of DNA that is heritable

2. People like some of the phenotypes produced by mutant alleles

3. Recessive Mutations

   • Phenotype is associated with the homozygous condition
   • Often involve the loss of gene function
     • Null / Amorphic Alleles
       • A nonfunctional protein is produced OR no protein is produced
     • Hypomorphic Alleles
       • A poorly functioning protein is produced OR reduced amounts of a normally functioning protein is produced

4. Dominant Mutations

   • Only need one copy of allele to see phenotype
   • Often involve gain/change of gene function
     • Dominant Hypermorphic Alleles
       • Negative phenotypic consequences due to the over-production of a normal protein OR negative phenotypic consequences due to the production of a protein with increased activity levels
     • Neomorphic Alleles
       • Negative phenotypic consequences due to the presence of an altered protein that has a new function

5. Silent Mutation: DNA change results in a new mRNA codon that specifies the same amino acid

6. Missense Mutation: DNA change results in a new mRNA codon that specifies a different amino acid

7. Nonsense Mutation: DNA change results in a new mRNA codon that is a STOP codon

8. Frameshift Mutation: DNA change that results in a change in the reading frame. Downstream from the insertion/deletion, the reading frame is shifted, which results in a very different amino acid sequence for the latter part of the protein

9. Sources of Mutations

   • Spontaneous: Changes in the nucleotide sequence as a result of errors in the DNA replication
   • Induced: Changes in the nucleotide sequence which result from exposure to radiation and mutagenic chemicals

10. Certain chemicals are mutagenic