Chapter 15 Quiz

Provide an overview of the information contained in the graph.

-By age 20, approximately 80% of the XP population has skin cancer. -For non-XP individuals, the chance of skin cancer increases as they age. -Individuals with XP are more likely to develop skin cancer in their youth than non-XP individuals. -XP individuals almost always develop skin cancer by age 40.

When the researcher examines the progeny with eye pigment that result from these crosses, she finds two different categories of flies.Some crosses produce flies with eye pigment and notched wings, as well as flies with eye pigment and normal wings.Other crosses produce flies with eye pigment and notched wings, but no flies with eye pigment and normal wings. What might explain these results? Select all statements that are true.

-Progeny with eye pigment have a P {miniwhite +} insertion they inherited from their father. -Progeny with notched wings inherited the non-deleted chromosome 3 from their mother. -Progeny with normal wings inherited the chromosome 3 with the deletion from their mother. -Progeny with normal wings and eye pigment have both a P {miniwhite +} insertion and the chromosome 3 with the deletion. -A cross that does not produce progeny with normal wings and eye pigment indicates that the P-element insertion has disrupted an essential gene in the region spanned by the deletion.

Which two repair processes are the most error prone?

-nonhomologous end joining -translesion DNA synthesis

Which repair process(es) use(s) a DNA polymerase?

-nucleotide excision repair -homologous recombination (synthesis-dependent strand annealing) -base excision repair -translesion DNA synthesis

Trinucleotide repeat disorders are hereditary diseases caused by mutant genes containing an increased number of repeats of a DNA trinucleotide sequence. Which sequence(s) contain a trinucleotide repeat? Select all that apply.

.AGCGACAGCAGCAGCAGCAGCAAGT... ...CACGGCGGCGGCGGCGGCATCGC... ...CACGGAAGAAGAAGAAGAAATAGAC...

In the mid-1960s, George Streisinger proposed that strand slippage during DNA replication (shown in the figure) altered the number of DNA repeats found in trinucleotide repeat disorders. Formation of a hairpin structure in the region of repeated DNA during strand slippage could facilitate this process. Which trinucleotide repeat disorder would not be consistent with the hairpin formation part of this model?

Friedreich ataxia (GAA repeat)

Which enzyme is responsible for proofreading during replication?

dna polymerase

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.

false

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?

frameshift

Describe two possible interpretations.

1.One might suggest that transposons are more likely to insert in noncoding regions of the genome because they are more stable in such regions. 2. It is possible that transposons insert randomly and that selection eliminates those that have interrupted coding regions of the genome. Since such regions are more likely to influence the phenotype, selection is more likely to influence such regions.

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.

5' - T A A - 3'3' - A T T - 5' 5' - C A A - 3'3' - G T T - 5'

Why is a random mutation more likely to be deleterious than beneficial?

A functional sequence of nucleotides, a gene, is likely to be the product of perhaps a billion or so years of evolution. Each gene and its product function in an environment that has also evolved. A coordinated output of each gene product is required for life. Deviations from the norm, caused by mutation, are likely to be disruptive because of the complex and interactive environment in which each gene product must function. However, on occasion a beneficial variation occurs.

For which codon(s) could a single base change account for this amino acid change?Lysine to Asparagine

AAA and AAG

Compare and contrast between the following types of mutations: missense, nonsense, silent, and neutral.

All of these mutations are base substitutions. Missense mutations change one amino acid to another amino acid. Nonsense mutations change an amino acid coding codon to a stop codon. Silent mutations change an amino acid coding codon to a codon that codes for the same amino acid (due to the degeneracy of the genetic code). Neutral mutations change a codon to a different amino acid, but it has no effect on the protein's function.

For which codon(s) could a single base change account for this amino acid change?Leucine to Glutamine

CUG and CUA

Which of the following statements about deamination is true?

Deamination is induced by nitrous acid.

Assume that a new mutation occurs in the germ line of an individual. What finding would suggest that the new mutation is dominant rather than recessive?

If the new mutation were dominant and passed to the next generation, it would be expressed. New recessive mutations are not normally expressed in the next generation unless, through a combination with a like mutation from the other parent, they are homozygous

The researcher then crosses the F1 males (XP{miniwhite+}/ Y; transposase / +) to female flies that are homozygous for the white mutation. She selects F2 males that have eye pigment present (indicating that they have a P {miniwhite +} insertion somewhere in their genome). Why does the researcher select these F2 males? Select all statements that are true.

In this cross, most F2 males will have no eye pigment because they cannot inherit the X chromosome that had the original P {miniwhite +} insertion on it. In this cross, F2 males with eye pigment result from the P-element moving to a new location on an autosome.

How may it lead to a mutation?

It allows hydrogen bonding of normally noncomplementary bases.

Adenine methylase is an enzyme used during mismatch repair (MMR). It helps determine which strand needs to be repaired by discriminating between template and new DNA strand. If this enzyme is mutated, how would MMR be affected?

MMR would be hindered because both strands would be unmethylated and both would appear as new DNA strands and it would not be able to determine which strand has the error.

Which repair system uses the RecA and LexA proteins?

SOS repair

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?

T

What is tautomeric shift?

Tautomeric shift is an intramolecular proton shift that changes the bonding structure of the molecule.

Explain why individuals with XP show such an early age of onset.

XP individuals lack one or more genes involved in DNADNA repair.

A researcher is interested in screening for P-elements inserted into a region on chromosome 3. To produce new insertions, she crosses females homozygous for a miniwhite + P-element on the X chromosome with males homozygous for immobilized transposase on chromosome 2. What genotype will the F1 male flies have? (Note that a "+" indicates a wild-type chromosome without the transposase locus or the P {miniwhite +} insertion. The X /Y chromosomes are listed first, followed by the second chromosome.)

XP{miniwhite+}/ Y; transposase / +

Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene?

a frameshift deletion at the beginning of the gene

If a segment of DNA were replicated without any errors, the replicated strand would have the following sequence of nucleotides: 5' - ACTACGTGA - 3' Sort the following replicated DNA sequences by the type of point mutation each contains (frameshift, base substitution, or neither), as compared to the correct sequence shown above.

frameshift mutation -5'-ACTCGTGA-3' -5'-ACTTACGTGA-3' base substitution mutation -5'-ACTACGTGT-3' -5'-ACTAAGTGA-3' neither -none

What type(s) of mutations are likely produced by chemical #1?

frameshifts

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 | ...)

glutamine

For which codon(s) could a single base change account for this amino acid change?Alanine to Phenylalanine

none of these

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?

nonsense mutation

Which repair process in E. coli uses visible light to repair thymine dimers?

photoreactivation repair

What type(s) of mutations are likely produced by chemical #2?

transitions

What type(s) of mutations are likely produced by chemical #3?

transitions and frameshifts

What type(s) of mutations are likely produced by chemical #4?

transversions