GENETICS ESSENTIALS Concepts and Connections SECOND EDITION GENETICS ESSENTIALS Concepts and Connections SECOND EDITION Benjamin A. Pierce © 2013 W. H. Freeman and Company CHAPTER 13 Gene Mutations, Transposable Elements, and DNA Repair
CHAPTER 13 OUTLINE 13.1 Mutations Are Inherited Alterations in the DNA Sequence, Mutations Are Potentially Caused by a Number of Different Natural and Unnatural Factors, Transposable Elements Are Mobile DNA Sequences Capable of Inducing Mutations, A Number of Pathways Repair Changes in DNA, 358
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13.1 MUTATIONS ARE INHERITED ALTERATIONS IN THE DNA SEQUENCE The Importance of Mutations Categories of Mutations Types of Gene Mutations Phenotypic Effects of Mutations Suppressor Mutations
THE IMPORTANCE OF MUTATIONS Source of all genetic variation, which further provides the raw material for evolution Source of many diseases and disorders Useful for probing fundamental biological processes
CATEGORIES OF MUTATIONS Somatic Mutations Germ-line Mutations Gene vs. Chromosomal Mutations
TYPES OF GENE MUTATIONS (BASED ON THEIR MOLECULAR NATURE) Base substitutions Transition Transversion Insertions and deletions Frameshift mutations In-frame insertions and deletions
TYPES OF GENE MUTATIONS (BASED ON THEIR MOLECULAR NATURE) Expanding nucleotide repeats Increase in the number of copies of a set of nucleotides
PHENOTYPIC EFFECTS OF MUTATIONS Forward mutation: wild type mutant type Reverse mutation: mutant type wild type Missense mutation: amino acid different amino acid Nonsense mutation: sense codon nonsense codon Silent mutation: codon synonymous codon Neutral mutation: no change in function
PHENOTYPIC EFFECTS OF MUTATIONS Loss-of-function mutations Usually recessive Gain-of-function mutations Usually dominant Conditional mutations Require specific conditions Lethal mutations
SUPPRESSOR MUTATIONS Suppressor mutation: a mutation that hides or suppresses the effect of another mutation Intragenic Intergenic
Intragenic SUPPRESSOR MUTATIONS
Intergenic SUPPRESSOR MUTATIONS
MUTATION RATES Factors affecting mutation rates Variation in mutation rates Adaptive mutations
13.2 MUTATIONS ARE POTENTIALLY CAUSED BY A NUMBER OF DIFFERENT NATURAL AND UNNATURAL FACTORS Spontaneous and Induced Spontaneous Replication Errors Spontaneous Chemical Changes Chemically Induced Mutations Radiation
SPONTANEOUS REPLICATION ERRORS Tautomeric shifts Mispairing due to other structures Wobble pairing
Incorporation errors and replication errors SPONTANEOUS REPLICATION ERRORS
Causes of deletion and insertions Strand slippage SPONTANEOUS REPLICATION ERRORS
Causes of deletion and insertions Unequal crossing over SPONTANEOUS REPLICATION ERRORS
SPONTANEOUS CHEMICAL CHANGES Depurination: loss of purine
SPONTANEOUS CHEMICAL CHANGES Deamination: loss of an amino group
CHEMICALLY INDUCED MUTATIONS Mutagen Base analogs
CHEMICALLY INDUCED MUTATIONS Intercalating agents: proflavin, acridine orange, ethidium bromide, and dioxin
RADIATION Pyrimidine dimer: two thymine bases block replication. SOS system in bacteria: SOS system allows bacteria cells to bypass the replication block with a mutation-prone pathway.
13.3 TRANSPOSABLE ELEMENTS ARE MOBILE DNA SEQUENCES CAPABLE OF INDUCING MUTATIONS General characteristics of transposable elements: Flanking direct repeats Terminal inverted repeats
Movement of transposon from one location to another DNA transposons Retrotransposons Replicative transposons New copy is introduced on the new site, old copy remains on the original site Nonreplicative Transposons Excises from old site and inserts in a new one (no copy increase) TRANSPOSITION
The mutagenic effects of transposition: TRANSPOSITION
18.4 A NUMBER OF PATHWAYS REPAIR CHANGES IN DNA Mismatch Repair Direct Repair Base-excision Repair Nucleotide-excision Repair
18.4 A NUMBER OF PATHWAYS REPAIR CHANGES IN DNA Mismatch Repair
18.4 A NUMBER OF PATHWAYS REPAIR CHANGES IN DNA Direct Repair
18.4 A NUMBER OF PATHWAYS REPAIR CHANGES IN DNA Base-excision Repair DNA glycosylases Uracil glycosylase Nucleotide-excision Repair Removes bulky DNA lesions (pyrimidine dimers)
18.4 A NUMBER OF PATHWAYS REPAIR CHANGES IN DNA Genetics diseases and faulty DNA repair Xeroderma pigmentosum Hereditary non-polyposis colon cancer (HNPCC)