Chapter 14: Gene Mutation, DNA Repair, and Transposable Elements

• Mutations are usually, but not always spontaneous
• Mutations may be classified in various ways
• Genetic techniques, cell cultures, and pedigree analysis are all used to detect mutations
• The spontaneous mutation rate varies greatly among organisms
• Mutations occur in many forms and arise in different ways
• High-energy radiation penetrates cells and induces mutations
• Gene sequencing has enhanced understanding of mutations in humans
• The Ames test is uses to assess mutagenicity of compounds
• Organisms can counteract DNA damage and mutations by activating several types of repair systems
• Site-directed mutagenesis allows researchers to investigate specific genes
• Transposable genetic elements move within the genome and may disrupt genetic function

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Gene Mutations

Mutations were originally identified and defined by their effects on the phenotype.  Mutations can be defined in several ways.  A change in the number or arrangement of a chromosome is called a chromosomal mutation (or chromosomal aberration).  At the molecular level,  mutation can be defined as a heritable change in the nucleotide sequence of a gene.  Such mutations are caused by the substitution of one nucleotide for another and by the addition or deletion of one or more nucleotides in DNA.  Mutations that affect a single nucleotide pair in a DNA molecule are called point mutations.  Mutations can also be defined by their effect on the amino acid sequence of a protein

There are many types of mutations, and many different ways to classify them. A mutation may be a transition mutation or a transversion mutation, or may be silent or conservative, thanks to the organization of genetic code. Most deleterious mutations are either transversions, relative to transitions, or frame shifts resulting from base substitutions.