Chapter 13 Flashcards
Define mutation:
What are mutations the source of?
What are they useful for?
Inherited alterations in the DNA
sequence.
- 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
Somatic mutations:
mutation in a cell that does not
give rise to gametes
Germ-line mutations:
mutation in a germ-line cell
Somatic vs Germ-line
Germ cells pass on genetic information to the next generation, but somatic cells repair and reproduce only in one body. Somatic cells do not contribute to the creation of offspring, whereas germ cells do. Germ cells go through both meiosis and mitosis, whereas somatic cells only go through mitosis
What are the types of genetic mutation?
Base substitution (transition and transversion)
Insertions/deletions (indels)
Frameshift mutations (In-frame insertions and deletions)
Expanding nucleotide repeats
What are base substitutions? What is the difference between transition and transversion? What are the possible base changes for each?
Base substitutions are single pair of bases in DNA being altered.
Transitions: Purine to Purine or Pyrimidine to Pyrimidine.
Possible base changes: A to G, G to A; T to C, C to T
Transversions: Purine to Pyrimidine or Pyrimidine to Purine.
Possible base changes: A to C, A to T, G to C, G to T; C to A, C to G, T to A, T to G
What are indels? What are the two things that go with it?
A mutation named with the blend of insertion and deletion.
Insertion: An insertion changes the DNA sequence by adding one or more nucleotides to the gene
Deletion: A deletion changes the DNA sequence by removing at least one nucleotide in a gene
What are frameshift mutations?
A genetic mutation caused by a deletion or insertion in a DNA sequence that shifts the way the sequence is read.
Causes gene’s codes in groups of three to change, either an extra codon or not enough codons
What are expanding nucleotide repeats?
An increase in the number of copies of a set of nucleotides. Occurs when the number of triplets present in a mutated gene is greater than the number found in a normal gene
What are the ten phenotypic effects of mutations?
Forward mutation
Reverse mutation
Missense mutation
nonsense mutation
silent mutation
neutral mutation
loss-of-function mutation
gain-of-function mutation
conditional mutation
lethal mutation
What are forward mutations?
What are reverse mutations?
Wild type to mutant type
Mutant type to wild type
What are missense mutations?
Amino acid to different amino acid
What are nonsense mutations?
Sense codon to nonsense codon. Makes stop codon
What are silent mutations?
Codon to synonymous codon. No change in amino acid sequence
What are neutral mutations?
No change in function
What are loss-of-function mutations?
Complete or partial absence of normal protein function
What are gain-of-function mutations?
Produce a protein or gene product whose function is not normally present.
What is a conditional mutation?
Only expressed under certain conditions
What are lethal mutations?
Cause premature death
What are suppressor mutations?
A mutation that hides or suppresses the effect of another mutation.
What are double mutants?
The result of two simultaneous mutations.
What are intragenic mutations
Mutation within the same gene location
What are intergenic mutations?
Mutation within different location on the gene.
What are spontaneous mutations?
Natural changes in DNA structure or from replication error. Chemical changes to DNA
What are induced mutations?
Mutations made to happen
Mutations from an environmental agent such as a chemical or radiation
What are mutation rates?
What are three things that go with mutation rates?
The frequency with which a wild type allele at a locus changes into a mutant allele.
- Rates of spontaneous mutations are generally low
- Affected by environmental and genetic factors
- Variation in mutation rates between genes and
species
What does the Ames Test do?
Detects mutagens. Test used to see if a product is causes any mutations.
– Both cancer and mutations result from damage to DNA
– 90% of carcinogens are also mutagens
– Use bacteria as an indicator of carcinogenesis in humans
What are transposable elements? What kind of mutations may they cause?
Sequences that can move about the genome. May cause mutations (deletions, duplications, and inversions) “jumping genes”
What are the features of transposable elements? (Two types of repeats)
Flanking direct repeats: 3-12 bp long
Terminal inverted repeats: 9-40 bp long
How do transposable elements effect the genome?
They’re mobile DNA sequences that are capable of inducing mutations.
Generally speaking, what does DNA repair require? What is redundancy?
It requires two nucleotide strands of DNA- Template
More than one type of DNA damage can be repaired by more than one pathway of repair
What is mismatch repair?
Corrects mismatched nucleotides in DNA after replication
What is direct repair?
DNA repair in which modified bases are changed back into their original structures. It requires special enzymes for each type of repair
What is base-excision repair?
What do glycosylases do?
DNA repair that first excises modified bases using glycosylases and then replaces the entire nucleotide.
Glycosylases recognize
inappropriately paired
bases and breaks the
bond between the
base and the
deoxyribose group.
What is nucleotide-excision repair?
What are the proteins called? How is the cut-out sequence fixed? What seals the nick left by polymerase?
DNA repair that removes bulky DNA lesions and other types of DNA damage.
Proteins: Uvr for UV repair
DNA polymerase I fixes cut-out sequence
DNA ligase seals nicks
What are the two types of double strand repair?
(NOT the stuff with repeats)
Non-homologous end joining
Homologous Recombination
What does translesion DNA polymerase do?
Enable cells to tolerate many forms of DNA damage
What are genetic diseases (2) caused by faulty DNA repair? What do they mean?
Xeroderma pigmentosum: Autosomal recessive condition. Defects in nucleotide-excision repair. Sun sensitivity, leads to skin cancer
Cancer: Mismatch in DNA repair. High incidences of specific cancers (colon cancer, HNPCC)
