Chapter 10-Genetics Flashcards
Mutation
Heritable change in the base sequence of the genome of an organism
Mutant
Organism with a mutation, genotype differs from parents
Wild-type
Isolated from nature, can be gene or strain
What are some examples of genotype vs. phenotype? How do these examples relate to mutations?
The gene for histodinol phosphate aminotransferase, hisC codes for the protein HisC. Mutations in this gene are hisCI and hisC2
His+ and His- do different actions
What does His+ do?
Makes own histodine (histodine prototroph)
What does His- do?
Cannot make own histidine, requires histidine supplement (histidine auxotroph)
Mutant selection
Placing organisms under conditions that favor or inhibit growth of cells with certain phenotypes
Mutant screening
Procedure to evaluate many strains, but all strains are able to grow
Is antibiotics resistance selectable or screening?
It’s selectable
Is pigment production selectable or screening?
Must screen
What are two molecular bases for mutation?
- Induced-environmental cause
2. Spontaneous-errors in DNA replication
Transition
a point mutation that changes a purine nucleotide to another purine (A ↔ G) or a pyrimidine nucleotide to another pyrimidine (C ↔ T).
Transversion
the substitution of a (two ring) purine for a (one ring) pyrimidine or vice versa, in deoxyribonucleic acid (DNA).[1]
Frameshifts are due to what?
Due to insertions or deletions
Reversion
“Back mutation” that restores the original phenotype
Same-site revertant
Mutation at same site restores phenotype
Second-site revertant
Mutation at different site in DNA restores phenotype-supressor mutation
Supressor mutations
- Mutations in same gene (2nd frameshift mutation)
- Mutation in another gene that restores function
- Mutation in another gene that replaces non-functional enzyme with a functional one
Deletions, frameshift mutations are…
stable
Insertions are…
not as stable
What is removed during direct reversal during DNA repair?
An alkyl group
What are three ways of DNA repair?
- Direct reversal
- Repair of single-stranded damage
- Repair of double-strand damage
In addition to the removal of an alkyl group, what also happens during direct reversal?
Photoreactivation, which cleaves pyrimidine dimers
What is repaired during repair of single-strand damage?
Base excision and nucleotide excision
How does double-strand damage repair work?
Through recombination to repair
What is repaired during double-strand repair?
Cross-strand links and double-stranded break
Describe the rate of changes in mutation.
It is low, yet detectable.
What organism has enhanced DNA repair?
Deinococcus radiodurans
In what ways does Deinococcus radiodurans have enhanced DNA repair?
20x resistant to UV
200x ionizing radiation
What can cause an increased mutation rate?
Mutator strains in changing environments
What is the Ames Test?
It is a mutagenicity test for carcinogens.
What does the Ames Test test for?
It tests for mutagenic chemicals.
How does the Ames Test work?
It uses auxotrophs with point mutations so that reversion can occur (His-S. enterica or Trp- E.coli). Also, back mutants have colonies formed on minimal medium and they form more in presence of mutagen
Improvements to the Ames test
- Strains that use error-prone repair pathways don’t always give the best reading.
- Liver enzyme preparations to convert chemicals to active forms needs work.
What are 5 kinds of gene transfer?
- Recombination
- Transformation
- Conjugation
- Transduction
- Transposable elements
Recombination
DNA from two different sources exchange sections or are brought together into a single DNA molecule
What is formed by recombination?
Homologous DNA
How does recombination take place?
Crossing over
Transformation
Free DNA from the environment transforms competent cells
First discovery of transformation was by…
Frederick Griffith in 1928
Transformtion
Free DNA from the environment transforms competent cells
Transduction
Bacteriophage transfers DNA from one cell to another
Generalized transduction
Any gene on donor chromosome can be transferred
Specialized transduction
Only a specific set of bacterial genes are transferred due to mistakes in excision
Conjugation
Genetic exchange involving cell-to-cell contact
An F plasmid stands for
fertility
What can an F plasmid do?
Can synthesize F pilus and make able the mobilization of DNA for transfer
How is the uptake of another F plasmid prevented?
Alteration of surface receptors
Episome
plasmid that can integrate into the chromosome
F+ strain
nonintegrated plasmid
Hfr strain
plasmid integrated into genome
Why is gene transfer system development difficult in Archaea?
Due to extreme conditions and antibiotics are useless
What kind of gene transfer happens in Archaea?
Transformation, conjugation, and transduction
Mobile DNA, aka
transposable elements
Transposable elements
DNA that moves from one site to another within a DNA molecule
What are the insertion sequences of transposable elements like?
Short, 1000 nucleotides, inverted repeated of 10-50 base pairs
What protein is involved in the insertion sequence formation in transposable elements?
Transposase
Describe transposons.
Large
Inverted repeats
Transposase
Other genes
Transposon mutagenesis
Selection and screening of treated colonies follow
