Deck 14: Gene Mutation,DNA Repair,and Transposition

Question 1

Three major types of RNAs are mRNA,rRNA,and tRNA.For each of the conditions below,predict the consequences in terms of the population of proteins being synthesized in a particular cell.What qualitative and quantitative changes,if any,are expected in the individual protein involved (if one is involved)and in the population of proteins produced in that cell?
(a)A frameshift mutation in mRNA.The condition is heterozygous in the involved cell.
(b)A deletion (homozygous)that removes approximately half of the rRNA genes.

Answer 1

(a)Population of proteins: Half of the protein products of that gene will be defective,and the other half will be normal.Individual protein: The protein should show multiple amino acid substitutions "downstream" from the point of the mutation.If a nonsense triplet is introduced,the protein would be shortened in the substituted region.
(b)Population of proteins: There would be an overall reduction in protein synthesis.Individual protein: All the proteins would be made in their normal form,but at reduced levels.

Question 2

Conditional mutations are more likely to result from a mutation caused by which of the following alterations to the coding region of a gene?

A)four bases added within a short region of a gene
B)base addition
C)X rays
D)deletion
E)tautomeric shift

Answer 2

E

Question 3

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?

Answer 3

If dominant and if 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.

Question 4

List five general categories of mutation.

Question 5

Barbara McClintock discovered mobile elements in corn by analyzing the genetic behavior of two elements,Ds and Ac.The interplay between these two elements has become one of the most interesting stories of discovery in the field of genetics.How do Ds and Ac interact?

A)Ds causes a deletion next to the insertion site of Ac.
B)Ac causes a deletion next to the insertion site of Ds.
C)Ds moves only if Ac is present in the genome; Ac is capable of autonomous movement.
D)The movement of Ac is dependent on two forms of Ds.
E)Both elements can move only within chromosome 9.

Question 6

Transposons,or jumping genes,are DNA elements that move within the genome.In which organismic groups are transposons found?

A)bacteria
B)eukaryotes
C)mammals
D)ancient bacteria
E)all organismic groups

Question 7

Mutations may exert a variety of effects on living systems.List at least three categories of mutations based on their biological effects.

Question 8

How was it determined that X-rays are mutagenic?

Question 9

One type of mutation involves the replacement of a purine with a purine,whereas another causes the replacement of a pyrimidine with a purine or the reverse.What general terms are associated with these two mutational phenomena?

Question 10

Under which condition(s)might one have an amino acid substitution in a protein that does not result in an altered phenotype?

Question 11

A class of mutations that results in multiple contiguous amino acid changes in proteins is likely to be which of the following?

A)base analog
B)transversion
C)transition
D)frameshift
E)recombinant

Question 12

All insertion sequences (IS elements)contain two features that are essential for their movement.What are these two elements?

A)transposase and inverted terminal repeats
B)integrase and pseudogenes
C)integrase and oncogenes
D)proto-oncogenes and oncogenes
E)transposase and oncogenes

Question 13

Mutations that arise in nature,from no particular artificial agent,are called ________.

A)oblique mutations
B)induced mutations
C)spontaneous mutations
D)chromosomal aberrations
E)cosmic mutations

Question 14

Two formal terms used to describe categories of mutational nucleotide substitutions in DNA are ________.

A)base analogs and frameshift
B)error prone and spontaneous
C)transversions and transitions
D)euchromatic and heterochromatic
E)sense and antisense

Question 15

In general,mutation rates in humans occur in the range of ________ (frequency)per gamete per generation.

Question 16

DNA may be damaged from the by-products of normal cellular aerobic respiration.Name three of these electrophilic oxidants that are generally classified as reactive oxidants.

Question 17

Ultraviolet light causes pyrimidine dimers to form in DNA.Some individuals are genetically incapable of repairing some dimers at "normal" rates.Such individuals are likely to suffer from ________.

A)xeroderma pigmentosum
B)SCID
C)phenylketonuria
D)muscular dystrophy
E)Huntington disease

Question 18

Some bacterial transposons,known as Tn elements,are larger than insertion sequences (IS elements)and contain protein-coding genes that have human health significance.What might such a bacterial transposon contain?

A)drug resistance
B)oncogene
C)pseudogene
D)proto-oncogene
E)dissociation element

Question 19

Nutritional mutations can be defined as ________.

A)those mutations that do not allow a bacterium or fungus to grow on minimal medium but do allow growth on complete medium
B)those mutations that change the composition of the medium
C)those mutations belonging to the group called prototrophs
D)those mutations caused by site-specific mutagenesis
E)all strains that are not auxotrophic

Question 20

Which of the following name two mutagens that would be classified as base analogs?

A)acridine orange and proflavin
B)ethylmethane sulfonate and ethylmethylketone peroxide
C)ultraviolet light and cosmic radiation
D)5-bromouracil and 2-amino purine
E)hydroxyurea and peroxidase

Question 21

Considering the electromagnetic spectrum,identify likely mutagens from the following list: radio waves,microwaves,infrared,ultraviolet,X-rays,gamma rays,cosmic rays.

Question 22

Three human disorders-fragile-X syndrome,myotonic dystrophy,and Huntington disease-are conceptually linked by a common mode of molecular upset.Describe the phenomena that link these disorders.

Question 23

Assuming one mutational event in a gene,on average,which of the following mutagens or mutational conditions would be expected to cause the most damage to a protein synthesized by such a mutagenized gene: 5-bromouracil,2-amino purine,ethylmethane sulfonate,or frameshift?

Question 24

When X-rays penetrate cells,electrons are ejected from atoms of molecules.Stable molecules can be transformed into which two types of hazardous materials?

Question 25

How were insertion sequences (IS elements)first discovered?

Question 26

In a survey of 240,000 human births,six achondroplastic births were recorded to parents who were unaffected.Given that this form of dwarfism is caused by a fully penetrant,dominant,autosomal gene,what is the mutation rate?

Question 27

Which human condition is caused by unrepaired UV-induced lesions?

Question 28

Describe the action of the enzyme transposase.

Question 29

What is meant by the term photoreactivation repair?

Question 30

The process of error correction of mismatched bases carried out by DNA polymerases is called ________.

Question 31

Under certain conditions,the rate of mutation of a particular gene may be determined in humans.Name three properties of the mutation that would favor the most direct determination of mutation rate in humans.

Question 32

Apurinic sites (AP sites)involve a spontaneous loss of a(n)________ in an intact double-helix DNA molecule.

Question 33

Some mutagens cause genetic changes that can be "corrected" by reexposing cells to the same mutagen.Other mutagens do not behave in this way.Provide one example of each of these two types of agents and describe the mutational changes caused in DNA.Explain why some mutagens behave in one way,whereas others do not.

Question 34

It has been found that a particular "+ -" combination of frameshift mutations in gene X gives a wild-type phenotype,whereas a "- +" combination gives a mutant phenotype,even though the sites of insertion/deletion are the same.How might these results be explained?

Question 35

What is the common influence of ultraviolet light on DNA?

Question 36

Recent discoveries on causes of fragile-X syndrome,myotonic dystrophy,and Huntington disease indicate which type of genetic alteration?

Question 37

What is the Ames test,and how does it work?

Question 38

A mutation that occurs naturally,without exposure to a known mutagen,is called a ________.

Question 39

Describe the mutagenic action of the following two mutagens: 5-bromouracil and ultraviolet light.

Question 40

Recombinational repair is activated when damaged DNA has escaped repair and the distortion disrupts the process of replication.Which gene is responsible for recombinational repair?

Question 41

A missense mutation causes premature chain (protein)termination.

Question 42

Of the two cell lines that can contain a mutation in an organism,somatic line and germ line,the latter is more consequential to subsequent generations.

Question 43

Strand discrimination during the process of DNA repair is based on DNA methylation in E.coli.

Question 44

Loss-of-function mutations eliminate the function of a gene product and may be dominant or recessive.

Question 45

2-amino purine is an alkylating agent.

Question 46

Postreplication repair is a system that responds after damaged DNA has escaped repair and failed to be completely replicated.

Question 47

Although mutation is the original source of genetic variation,its influence on changing allelic frequencies is relatively minor.

Question 48

What are LINES?

Question 49

When treating an organism with a mutagen,although it is possible that homozygous mutations will occur,it is more likely that most new mutations will be heterozygous or hemizygous.

Question 50

Pyrimidine dimers are typically caused by the mutagen 2-amino purine.

Question 51

IS elements (insertion sequences)are stable DNA occupants of prokaryotic genomes that are not found among eukaryotes.

Question 52

The shorter the wavelength of a radiation source,the greater its likelihood of causing damage.

Question 53

Certain base analogs such as 5-bromouracil cause mutations by chemically altering nitrogenous bases in nonreplicating DNA.