Chapter 14 (Classes of mutation, explain all of them, know how tautomerization alters base pairing, know repair systems.)

If a pyrimidine replaces a pyrimidine or a purine replaces a purine, a ____________ has occured. If a purine replaces a pyrimidine, or vice versa, a ____________ has occured.

Transition Transversion

PS14 What type(s) of mutations are likely produced by chemical #2? transversions transitions frameshifts

Transitions Correct Mutations that are induced by chemical #2 could be reversed by mutagens that can create the same type of mutations. Since both EMS and 5-Bromouracil reversed the mutations created by chemical #2, and these mutagens create transition mutations, it is likely that chemical #2 also induces transition mutations. For example if chemical #2 induced an adenine-to-guanine transition mutation that gave rise to a mutant phenotype, then EMS could induce a guanine-to-adenine transition mutation to reverse the mutant phenotype.

PS14 What type(s) of mutations are likely produced by chemical #3? Select all that apply. transitions frameshifts transversions

Transitions and frameshift Correct Mutations that are induced by chemical #3 could be reversed by mutagens that can create the same type of mutations. Since all three mutagens reversed mutations created by chemical #3, it is likely that chemical #3 induces transition mutations as well as small deletions or insertions that result in frameshift mutations.

Mutagenesis.docx Explain how transposons work and why they increase genetic variation in populations.

Transposons are known as "jumping genes" that can move or transpose within and between chromosomes, inserting themselves into various locations within the genome. They alter gene-expression patterns in ways that are subsequently retained by the host.

PS14 What type(s) of mutations are likely produced by chemical #4? Select all that apply. transitions frameshifts transversions

Transversions Correct Mutations that are induced by chemical #4 could be reversed by mutagens that can create the same type of mutations. Since none of three mutagens reversed mutations created by chemical #4, it is likely that chemical #4 does not induce transition mutations or frameshift mutations. Chemical #4 does in fact induce mutations since exposing E. coli to chemical #4 resulted in observed mutant phenotypes. Because these mutant phenotypes were not reversed by any of the three mutagens, it is likely that chemical #4 induces a different type of mutation. The only remaining choice listed as a mutation type is transversions. In the future, a mutagen that induces transversion mutations could be used to determine if the chemical #4 mutations could be reversed.

Ch. 14 Quiz Many chemicals are more mutagenic after being processed in the liver. True False

True

PS14 For which codon(s) could a single base change account for this amino acid change? Lysine to Asparagine Select all that apply. Got to use table on flip side. a) AAG b) UUU c) AAA d) none of these codons

a and c

PS14 For which codon(s) could a single base change account for this amino acid change? Leucine to Glutamine Select all that apply. a) CUG b) CUU c) UUG d) CUA e) CUC f) UUA g) none of these codons

a and d

PS14 Which sequence(s) contain a trinucleotide repeat? Select all that apply. a)...AGCGACAGCAGCAGCAGCAGCAAGT... b)...CACGGCGGCGGCGGCGGCATCGC... c)...GGCAGGCAGGCAGGCAGGCAGGCTG... d)...TTCACTGTCACTGTCACTGTCACTGTCC... e)...CACGGAAGAAGAAGAAGAAATAGAC...

a b e

PS14 Huntington's disease occurs when a CAG repeat expansion in the coding region of the HTT gene becomes too long. The CAG repeat is also in frame. (... | CAG | CAG | CAG | ...) Which amino acid is coded for in this repeat? a) glutamine b) proline c) glutamic acid d) asparagine

a) glutamine

PS14 Suppose that the transient rare guanine tautomer shifted back to the common guanine tautomer prior to a second round of replication. Which DNA sequence(s) would be present in the sister chromatids after this second round of replication? Select all that apply. Which DNA sequence(s) would be present in the sister chromatids after this second round of replication? Select all that apply. a) 5' - C G G - 3' 3' - G C C - 5' b) 5' - T A A - 3' 3' - A T T - 5' c) 5' - T A A - 3' 3' - G T T - 5' d) 5' - U A A - 3' 3' - A U U - 5' e) 5' - C A A - 3' 3' - G T T - 5' f) none of these

b) 5' - T A A - 3' 3' - A T T - 5' and e) 5' - C A A - 3' 3' - G T T - 5' After the first round of DNA replication, the DNA sequence of the sister chromatids will be: (Note: G* is the rare guanine tautomer.) 5' - CAA - 3' 3' - GTT - 5' 5' - TAA - 3' 3' - G*TT - 5' After transient rare guanine tautomer shifted back to the common guanine tautomer prior to a second round of replication, the DNA sequence of the sister chromatids will be: (Note: Italics represent the template strand used during the second DNA replication.) 5' - TAA - 3' 3' - ATT - 5' 5' - CAA - 3' 3' - GTT - 5' (Note that this sister chromatid is present after the first replication and after the second replication.) Now a permanent mutation has been incorporated into one of the sister chromatids as a result of a tautomeric shift.

PS14 Which repair system uses the RecA and LexA proteins? a) Photoreactivation repair b) SOS repair c) Mismatch repair d) Proofreading repair

b) SOS repair

PS14 Suppose that a transient tautomeric shift occurred in the guanine base to produce a rare tautomer in the partial DNA sequence just prior to a round of DNA replication. Which base would be added opposite this rare tautomer during DNA replication? Which base would be added opposite this rare tautomer during DNA replication? a) A b) T c) U d) G e) C

b) T When the replicative polymerase encounters this rare guanine tautomer, thymine is added to the newly synthesized strand instead of cytosine.

PS14 Which of the following statements most accurately describes the transposable genetic elements found in corn? a) Transposable elements found in maize are strictly autonomous. b) The earlier in kernel development a reversion event occurs, the larger the spot of tissue exhibiting the reversion phenotype. c) Transposons in corn lack inverted repeats. d) Transposable elements are found only in corn.

b) The earlier in kernel development a reversion event occurs, the larger the spot of tissue exhibiting the reversion phenotype.

Ch. 14 Quiz Why would a mutation in a somatic cell of a multicellular organism escape detection? a) Most somatic mutations are recessive and do not cause a phenotypic change in the cell. As a result, it is highly unlikely that the organism will be sufficiently altered to respond to a screen. b) When conducting genetic screens, it is assumed that all the cells are genetically identical. Since a somatic mutation first appears in a single cell, it is highly unlikely that the organism will be sufficiently altered to respond to a screen because none of the other cells will have the mutation. c) Most somatic mutations are dominant and do not cause a phenotypic change in the cell. As a result, it is highly unlikely that the organism will be sufficiently altered to respond to a screen. d) A somatic mutation is a type of mutation that can be easily repaired. Therefore, the mutation is often corrected before the genetic screen takes place.

b) When conducting genetic screens, it is assumed that all the cells are genetically identical. Since a somatic mutation first appears in a single cell, it is highly unlikely that the organism will be sufficiently altered to respond to a screen because none of the other cells will have the mutation.

Ch. 14 Quiz In the Ames Test, the appearance of his+ revertants in the presence of a non-mutagenic control compound indicates that _______. a) the growth medium contains factors that are mildly mutagenic b) some of the reversion mutations are not caused by the mutagen being tested c) there is some low-level contamination in most experiments d) liver extract increases the potency of some mutagens

b) some of the reversion mutations are not caused by the mutagen being tested

Ch. 14 Quiz The purpose of the Ames Test is to _______. a) determine whether Salmonella typhimurium his- mutants can revert to his+ b) test the mutagenic effects of chemicals c) determine whether histidine has mutagenic effects in S. typhimurium d) study how the liver affects potential mutagens

b) test the mutagenic effects of chemicals

PS14 Which enzyme is responsible for proofreading during replication? a) DNA ligase b) DNA glycosylase c) DNA polymerase d) RNA polymerase

c) DNA polymerase

PS14 It has been observed that diseases caused by repeat expansions are the result of trinucleotide repeats rather than smaller or larger repeat lengths. If non-trinucleotide repeat expansions were present in the coding region of a gene, which type of mutation would you expect to be the most likely? a) nonsense b) missense c) frameshift d) silent

c) frameshift Repeat lengths that are not multiples of three in the coding regions of genes would likely cause frameshift mutations, rendering the protein product nonfunctional. Two mutant alleles may not be developmentally viable; thus these genotypes do not survive to pass on these alleles.

PS14 Suppose that the top strand is the coding (nontemplate) strand and the three bases shown represent a single in frame codon in a gene. What will be the effect of the tautomeric shift-induced mutation on the amino acid sequence? a) missense mutation b) silent mutation c) nonsense mutation d) not enough information to determine

c) nonsense mutation

PS14 Which trinucleotide repeat disorder would not be consistent with the hairpin formation part of this model? CG AA GC CG AA GC CG A a) Huntington disease (CAG repeat) b) Fragile X syndrome (CGG repeat) c) Jacobsen syndrome (CGG repeat) d) Friedreich ataxia (GAA repeat)

d) Friedreich ataxia (GAA repeat)

PS14 The purple spots on colorless background of corn kernels observed by Barbara McClintock were the result of _______. a) environmental factors b) transposition of the Ds elements into the color gene c) mutation in the transposase gene d) transposition of the Ds elements out of the color gene

d) transposition of the Ds elements out of the color gene https://quizlet.com/24212449/genetics-ch-13-flash-cards/

Ch. 14 Quiz A point mutation occurs such that a codon is changed from AGA to AGC. Which term describes this mutation? See Section 14.1 ( page 258) . a) transition mutation b) frameshift mutation c) insertion mutation d) transversion mutation

d) transversion mutation

PS14 For which codon(s) could a single base change account for this amino acid change? Alanine to Phenylalanine Select all that apply. a) GCG b) GCC c) GCU d) GCA e) none of these codons

e does not overlap at all

PS14 Autonomous elements can transpose by themselves even though they cannot produce transposase. T/F

false

Mutagenesis.docx What are the different ways mutations are classified?

(Type of molecular change) (Classification based on phenotypic effects) (Classification based on Location of Mutation)

Ch. 14 Quiz 2-amino purine is an alkylating agent. True False

False

Mutagenesis.docx What are the different ways mutations are classified? (Type of molecular change)

Classification based on type of molecular change. Point mutation/base substitution: a change of one base pair to another in a DNA molecule Missense mutation: A change of one nucleotide of a triplet resulting in a new triplet that codes for a different amino acid. Nonsense mutation: Triplet changes into a stop codon, resulting in the termination of translation of the protein. Silent mutation: Mutation that alters a codon but does not change the amino acid at the position in the protein. Frameshift mutation: insertion or deletion of one or more nucleotides at any point within the gene.

Mutagenesis.docx What are the different DNA repair systems? How do their activities differ? Be sure you can discuss these activities: Double-stranded break repair

Double-stranded break repair: Reattach two broken DNA strands. Usually occurs during the late S or early G2 phase of the cell cycle, after DNA replication, a time when sister chromatids are available to be used as repair templates.

Mutagenesis.docx Explain how different mutagens alter DNA.

During SOS repair, DNA synthesis becomes error-prone, inserting random and possibly incorrect nucleotides in places that would normally stall DNA replication. Although, it may allow the cell to survive DNA damge that would have otherwise killed it. UV light is mutagenic as the result of the creation of pyrimidine dimers. Photoreactivation enzymes (PRE's) work to cleave the bonds between thymine dimers, thus directly reversing the effect of UV radiation.

Why is EMS a mutagen of choice for genetic research? What would the effects of EMS in a strain of Drosophila lacking functional mismatch repair systems.

EMS alkylates the keto groups at the sixth position of guanine and at the fourth position of thymine. Altered bases are not readily repaired, and once the transition to normal bases occurs through replication, such mutations avoid repair altogether.

Ch. 14 Quiz Certain base analogs such as 5-bromouracil cause mutations by chemically altering nitrogenous bases in nonreplicating DNA. True False

False

PS14 Bacteria can distinguish between a newly replicated DNA strand and the original template strand because the newly replicated strand is methylated, whereas the original template strand is not. T/F

False: Methylation occurs shortly after replication, so the original template strand is methylated and the newly replicated DNA strand is not. https://quizlet.com/104450307/honors-genetics-chapter-15-flash-cards/

PS14 What type(s) of mutations are likely produced by chemical #1? frameshifts transitions transversions

Frame shift Correct Mutations that are induced by chemical #1 could be reversed by mutagens that can create the same type of mutations. If chemical #1 induced frameshift mutations by making small deletions or insertions, then acridine orange (which also induces frameshift mutations) could restore the proper reading frame with a second mutation. Since acridine orange is the only mutagen that reversed the mutations, then it is likely that chemical #1 induces frameshift mutations.

Mutagenesis.docx What are the different ways mutations are classified? (Classification based on phenotypic effects)

Loss-of-function mutation: reduces or eliminates the function of the gene product. Null mutation: Mutation that result in the complete loss of function of a gene. Recessive mutation: Results in a wilde-type phenotype when present in a diploid organism and the other allele is wild type. Dominant mutation: Two affects, haploinsufficiency, which loss of function mutation and dominant gain-of-function mutation Dominant negative mutation: Mutant nonfuctional gene product binds to the wild-type gene product, inactivating it. Visible mutations: phenotypically visible Nutritional mutation: loss of ability to synthesize an amino acid or vitamin. Behavioral mutations: behaviorally noticeable. Regulatory mutations: affect the regulation of gene expression. Conditional mutations: enviornmental mutation where the organism finds itself Temperature-sensitive mutation: form of conditional mutation. Neutral mutaiton: can occur either in a protein-coding region or in any part of the genome, and has little effect on the genetic fitness of the organism.

Mutagenesis.docx What are the different DNA repair systems? How do their activities differ? Be sure you can discuss these activities: Photoreactivation repair Base excision repair Nucleotide excision repair (XP mutants) Double-stranded break repair

Photoreactivation repair: Light-induced repair of damage caused by exposure to ultraviolet light. Associated with an intracellular enzyme system. Human and other organisms lack photoreactivation repair and must rely on other repair mechanisms. Nucleotide excision repair: Removal of damaged DNA segments followed by repair synthesis with the correct nucleotide sequence. Remove "bulky" lesions in DNA that alter or distort the double helix. Could be the UV-induced pyrimidine dimers or DNA adducts. XP mutants: A rare recessive genetic disorder that predisposes individuals to severe skin abnormalities, skin cancers, and a wide range of other symptomes including developmental and neurological defects. Patients with XP are extremely sensitive to UV radiation in sunlight.

Mutagenesis.docx What are the different DNA repair systems? How do their activities differ? Be sure you can discuss these activities: Proof-reading Mismatch repair SOS repair

Proofreading: DNA polymerase proofreads each step, catching 99 percent of those errors. If an incorrect nucleotide is inserted during polymerization, the enzyme can recognize the error and "reverse" its direction. It then behaves as a 3' to 5' exonuclease, cutting out the incorrect nucleotide and replacing it with the correct one. Mismatch repair: Errors such as base-base mismatches, small insertions, and deletions that remain after proofreading, mismatch repair is now activated. Mismatches are detected, the incorrect nucleotide is removed, and the correct nucleotide is inserted in its place. SOS repair: Responds to damaged DNA, it is a last resort to minimize DNA damage. DNA synthesis becomes error-prone, inserting random and possibly incorrect nucleotides in places that would normally stall DNA replication. As a result, SOS repair itself becomes mutagenic even though it may allow the cell to survive DNA damage that would otherwise kill it.

Mutagenesis.docx What are the different ways mutations are classified? (Classification based on Location of Mutation)

Somatic mutations: Those occuring in any cell in the body except germ cells Autosomal mutation: mutations on the autosomes. X-linked/Y-linked mutation: located on X or Y chromosomes

Mutagenesis.docx Explain how trinucleotide repeats cause some genetic diseases.

Specific short DNA sequences repeated many times. An example of a disease associated with these trinucleotide repeat expansions are Fragile-X syndrome, myotonic systrophy, and huntington disease. When the repeats occur outside coding regions, but within mRNA, mRNA's act as "toxic" RNAs that bind to important regulatory proteins, sequestering them away from their normal functions in the cell. Regions of DNA containing the repeats may become abnormally methylated, leading to silencing of gene transcription.