We have previously defined the four characteristics
or functions ascribed to the genetic information
as replication, storage, expression, and
variation by mutation. In a sense, mutation is a failure to
store the genetic information faithfully. If a change occurs
in the stored information, it may be reflected in the expression
of that information and will be propagated following
replication. Historically, the term mutation includes
both chromosomal changes and changes within single
genes. (Changes in chromosomes are collectively referred
to as chromosomal aberrations.) In this chapter we are
concerned with gene mutations. A change may be a simple
substitution of one nucleotide, or may involve the
insertion or deletion of one or more nucleotides within
the normal sequence of DNA.
Mutations form the basis for genetic studies. The resulting
phenotypic variability enables geneticists to identify
and study the genes that control the traits that have been
modified. Without the phenotypic variability that mutations
provide, genetic analysis would be impossible. For
example, if all pea plants displayed a uniform phenotype,
Mendel would have had no basis for his experimentation.
Because of the importance of mutations, great attention
has been given to their origin, induction, and classification.
Certain organisms lend themselves to induction of mutations
that can be detected easily and studied throughout
reasonably short life cycles. Viruses, bacteria, fungi, fruit
flies, other invertebrates, certain plants, and mice fit these
criteria. Thus, these organisms have been widely used to
study mutation and mutagenesis, and through other studies
they have also contributed to more general aspects of
genetic knowledge.
Once we have discussed mutation, we will turn our attention
to two related topics—DNA repair and transposable
genetic elements. These topics are logical extensions of
our consideration of gene mutation. Repair processes
serve to counteract mutation. Transposable genetic elements
often disrupt the normal structure of the gene and
therefore create mutations.
- 15.1 Mutations May Be Classified in Various Ways
- Spontaneous versus Induced Mutations
- Gametic versus Somatic Mutations
- Other Categories of Mutation
- 15.2 Genetic Techniques, Cell Cultures, and Pedigree
Analysis Are All Used to Detect Mutations
- Detection in Bacteria and Fungi
- Detection in Drosophila
- Detection in Plants
- Detection in Humans
- 15.3 The Spontaneous Mutation Rate Varies Greatly
Among Organisms
- 15.4 Mutations Occur in Many Forms and Arise in
Different Ways
- Tautomeric Shifts
- Base Analogs
- Alkylating Agents
- Acridine Dyes and Frameshift Mutations
- Apurinic Sites and Other Lesions
- 15.5 Ultraviolet and Ionizing Radiation are Mutagenic
- 15.6 Gene Sequencing Has Enhanced Understanding
of Mutations in Humans
- ABO Blood Types
- Muscular Dystrophy
- Trinucleotide Repeats in Fragile-X Syndrome, Myotonic Dystrophy, and Huntington Disease
- 15.7 The Ames Test Is Used to Assess the Mutagenicity
of Compounds
- 15.8 Organisms Can Counteract DNA Damage by
Activating Several Types of Repair Systems
- Photoreactivation Repair: Reversal of UV Damage
in Prokaryotes
- Excision Repair in Prokaryotes and Eukaryotes
- Xeroderma Pigmentosum and Nucleotide Excision
Repair
- Proofreading and Mismatch Repair
- Post-replication Repair and the SOS Repair System
- Double-Strand Break Repair in Mammals
- 15.9 Site-Directed Mutagenesis Allows Researchers to
Investigate Specific Genes
- Knockout Mutations and Transgenes
- 15.10 Transposable Genetic Elements Move Within the
Genome and May Disrupt Genetic Function
- Insertion Sequences
- Bacterial Transposons
- The Ac–Ds System in Maize
- Copia and P Elements in Drosophila
- P Element Transposons in Drosophila
- Transposable Genetic Elements in Humans
