Mutations Flashcards
Mutations which affect the individual and are not passed on
Somatic Mutations
Mutations which (normally) do not affect the individual but are passed on to children
Germ-line Mutations
Mutations that enhance or reduce the organism’s survival and reproductive abilities are called…?
Selective Mutations
Mutations that do not change the organism’s survival and reproductive abilities are called…?
Neutral Mutations
Two general classifications for mutations…?
Base Substitutions and Length Mutations
A change in the DNA sequence that does not change the amino acid sequence
Silent (Synonymous) Mutations
A change in the DNA that causes the substitution of an amino acid for another one
Missense (Nonsynonymous) Mutations
A change in the DNA that creates a new stop codon
Nonsense Mutations
A mutation that eliminates a stop codon
Read Through Mutation
A mutation that modifies an intron splice site
Cryptic Mutation
Sickle cell anemia is an example of which type of mutation?
Missense Mutation
A change in cis-elements that turns off gene expression
Suppression
A change in cis-elements that expresses a gene in the wrong place
Ectopic Expression
A change in cis-elements that expresses a gene at the wrong time
Ecchronic Expression
TRED stands for…
Trinucleotide Repeat Expansion Diseases
Common TREDs
Huntington’s Disease - CAG (>37)
Fragile-X - CGG (>200)
Friedreich’s Ataxia - GAA (>100)
Myotonic Dystrophy - CTG (>50)
The process of TREDs expanding and becoming worse through generations
Genetic Anticipation
Two types of base substitutions…?
Transition (A to G, G to A, C to T, or T to C)
Transversion (A to C/T, T to A/G, C to G/A, or G to C/T)
Tautomeric Shifts
A and C shift from amino to imino
G and T shift from keto to enol
Can lead to transition mutations
Base Analogs
Molecules similar to bases are added and have more frequent tautomeric shifts, leading to transitions
Ex: 5-bromouracil (5-BU) is a thymine analog and 2-aminopurine (2-AP) is an adenine analog
Mutagenic Agents
Cause bases to become base analogs or interfere with normal pairing
Ex: Deamination by nitrous acid or sodium bisulfite (G blocks replication, C becomes U, and A becomes hypoxanthine)
Ex: Alkylating agents lead to base substitutions, e.g. ethylmethane sulfonate (EMS)
Intercalating Agents
Chemicals that insert themselves into the DNA stack, blocking replication and transcription
Ex: Ethidium bromide, Proflavin, Acridine Orange
Thymine Dimers
Adjacent T bases will dimerize to cyclobutane rings when exposed to UV light; replication adds a base to these areas to create frameshift mutations
DNA Polymerase Proofreading/Mismatch Repair
DNA polymerase can recognize a mismatch, excise it, and replace it with the correct nucleotide
Direct Repair
Changes nucleotides to correct structures; repairs dimerization and some base analogs
Base Excision Repair
Fixes abnormal or modified bases by replacing entire nucleotide
Nucleotide Excision Repair
- Recognition (enzyme finds and tags mutation)
- Excision (Several bases around damage are excised by exonucleases)
- Replacement (Polymerase comes in to replace area
- Ligase (Repairs nicks)
Ways to repair thymine dimers
Photo Reactivation (Photolyase uses blue light to repair) Nucleotide Excision Repair (UvrABC binds to 12-base region and endonuclease removes it) Post Replication Repair (Occurs during replication to fix inability to replicate across dimer)
Disease caused by inability to repair thymine dimers
Xeroderma pigmentosum
