Deck 15: Genetics of Bacteria and Bacteriophages

Question 1

The E.coli chromosome is

A)linear.
B)circular.
C)single-stranded.
D)less than a megabase in length.
E)compartmentalized within an intracellular membrane.

Answer 1

B

Question 2

In general,transformation of most genes occurs at a frequency of one in every ________ cells.

A)10
B)100
C)1,000
D)10,000
E)1,000,000

Answer 2

C

Question 3

An arg^- strain of E.coli is transformed with a plasmid carrying the wild-type (arg⁺)gene.The transformed cells are replica-plated to two minimal medium plates: one supplemented with arginine and one lacking arginine.The transformed cells would grow on

A)only the plate supplemented with arginine.
B)only the plate lacking arginine.
C)both plates.
D)neither plate.
E)the plate supplemented with arginine,but only if a mutation occurred.

Answer 3

C

Question 4

________ bacterial strains require nutritional supplements to grow in a minimal medium.

A)Autotrophic
B)Prototrophic
C)Phototrophic
D)Heterotrophic
E)Auxotrophic

Question 5

In a genetic cross between two bacteriophage T4 rII mutants,r⁺ recombinants are produced.The genetic changes in these two rII mutants must be

A)heterozygous.
B)heteroallelic.
C)homozygous.
D)homoallelic.
E)polymorphic.

Question 6

Which of the following has episomal DNA inserted in the cell's chromosome?

A)An F⁺ cell
B)An F' plasmid
C)An Hfr cell
D)An F^- cell
E)All except D

Question 7

A plasmid such as an F factor that is capable of integrating into the bacterial chromosome is a(n)

A)prophage.
B)episome.
C)auxisome.
D)perisome.
E)elaiosome.

Question 8

Conjugation by which of the following with an F^- cell results in a cell that remains F^-?

A)F⁺
B)Hfr
C)F
D)A and C
E)B and C

Question 9

In E.coli,λ DNA integrates into which site on the bacterial chromosome?

A)ori
B)trp
C)bio
D)gal
E)att

Question 10

In the lysogenic bacteriophage life cycle,the λ chromosome

A)replicates and the phage genes take over the bacterium.
B)inserts itself physically into the host cell's chromosome.
C)expresses a repressor protein gene that inhibits the lytic pathway.
D)is replaced by a piece of bacterial DNA when packaged inside phage progeny.
E)Both B and C

Question 11

Which of the following statements is true regarding a temperate phage?

A)It can reproduce at warm or cool temperatures.
B)It is required for transformation.
C)It can be lytic or lysogenic.
D)It causes bacterial cells to conjugate.
E)It reproduces by binary fission.

Question 12

When Lederberg and Tatum performed their experiments on gene transfer in bacteria that lead to our understanding of conjugation,what were their controls?

A)They mixed strains A and B together.
B)They put strain A on one side of a U-shaped tube and strain B on the other,with a filter between them.
C)They found bio^- met^- cells.
D)They plated strain A and strain B separately onto minimal media plates to screen for spontaneous prototrophs.
E)They observed mating bridges with transmission electron microscopes.

Question 13

Which of the following methods can be used to create competent bacterial cells?

A)Treating the cells chemically
B)Exposing cells to a strong electric field
C)Making the cell membrane more permeable to DNA
D)Allowing the culture to enter stationary phase growth
E)A,B,and C only

Question 14

Minimal media is

A)growth media used in the smallest volume in which cells can grow.
B)growth media designed to minimize the growth of contaminants.
C)growth media that contains the minimal nutritional requirements for normal cells.
D)a way to visualize new mutations in a minimum amount of time.
E)used to reveal only mutant cell colonies against a dark background.

Question 15

To grow on artificial medium,prototrophic bacteria require

A)sunlight.
B)amino acid supplements.
C)vitamin supplements.
D)All of these
E)None of these

Question 16

E.coli strains that are Hfr

A)are easily mutated.
B)are susceptible to infection by bacteriophage.
C)contain the F factor integrated in the bacterial chromosome.
D)cannot be made competent.
E)have a low frequency of recombination.

Question 17

Cotransductants can be detected when the transduced genes are

A)closely linked.
B)far apart on the same chromosome.
C)on different chromosomes.
D)mutant.
E)Both B and D

Question 18

mtl,polA,and xyl are bacterial genes that can be transmitted using an Hfr strain.An interrupted mating experiment resulted in xyl exconjugants appearing at 7 minutes and reaching maximum level by 30 minutes.The mtl gene function exconjugants appeared at 11 minutes and leveled off at 80% maximum by about 33 minutes,while polA did not appear until 24 minutes into the experiment and then only slowly rose to about 30%.Which of the following shows the gene order with the insertion site (arrow)location correctly?

A)xyl mtl polA →
B)polA mtl xyl →
C)mtl xyl polA →
D)mtl polA xyl →
E)None of these

Question 19

The reason that many plasmids used in laboratories for transformation experiments contain an ampicillin resistance gene (amp_R)is

A)so that the plasmid can replicate in bacterial cells.
B)so that the plasmid can recombine with the bacterial genome.
C)to enable the recipient cell to conjugate.
D)to provide a selectable marker.
E)to map point mutations.

Question 20

What are temperate bacteriophages?

Question 21

Genetic mapping experiments performed by Seymour Benzer on rII mutants in the T4 phage showed that the gene is indivisible by the process of mutation and recombination.

Question 22

Cotransductant bacteria can occur if

A)a bacterial cell picks up two fragments of DNA from the environment,each with a different gene.
B)double crossover occurs between prophage DNA and the bacterial chromosome.
C)two genes are closely linked enough so that they can be packaged into a phage head and injected into a cell by a single phage.
D)two genes are introduced into the same bacterium by simultaneous infection with two different phages.
E)Both C and D

Question 23

In genetic exchange by conjugation,a single Hfr strain will transfer the entire bacterial chromosome to the recipient,allowing mapping in minutes from the first gene entering to the last one before the other half of the inserted F factor.

Question 24

To enhance the efficiency of transformation,bacterial cells can be induced to take up DNA by a strong electrical field.

Question 25

An Hfr strain of E.coli with the genotype a^+b+c+d+e+f+ is mated with an F^- auxotrophic strain with the genotype a^-b-c-d-e-f-.Conjugation is stopped at 10-minute intervals and the genotypes of the resulting conjugants are determined.The following results are obtained:
After 10 minutes e⁺
After 20 minutes a^+e+
After 30 minutes a^+b+e+
After 40 minutes a^+b+d+e+
After 50 minutes a^+b+c+d+e+
After 60 minutes a^+b+c+d+e+f+
What is the correct order of genes on this bacterial chromosome?

Question 26

In F⁺ × F^- crosses,none of the bacterial chromosome is transferred; only the F factor is.

Question 27

In a bacterial species genes q,r,s,and t were mapped in minutes through interrupted mating experiments.The results placed q and s on the two outer ends,but r and t were not resolvable by minutes.You have discovered no phage that can infect this species.If you have a q r s t Hfr strain and a q^{- r- s- t-} F^- strain,how could you measure the distance between the genes in map units?

Question 28

Explain how an F' × F^- conjugation can produce a partially diploid bacterial cell.

Question 29

What is the difference between generalized and specialized transduction? Give an example of specialized transduction.

Question 30

During a cis-trans complementation assay,two lac^- strains of bacteria are crossed.The progeny cells exhibit a lac^- phenotype.What does this indicate?

Question 31

Genetic exchange in bacteria by transduction requires cell-to-cell contact.

Question 32

A complete bacterial medium contains only the nutrients required for the growth of wild-type cells.

Question 33

A merodiploid cell has two copies of one or a few genes and only one copy of all the others.

Question 34

In the case of genetic exchange in bacteria by transformation,there is an exchange of DNA back and forth between cells,and a complete diploid cell is formed.

Question 35

In a series of cotransformation experiments,DNA fragments from x^+y+z+ donor bacteria were used to transform xyz recipient bacteria.The following transformation phenotypes were observed in the recipient cells:
xy^{+z
xyz+
x+y+z
x+yz+}
What does this imply about the gene order of x,y,and z?

Question 36

For a P1 transduction experiment,an E.coli donor strain with the genotype arg⁺,ser⁺,amp^R and a recipient strain with the genotype arg^-,ser^-,amp^S were used.The following results were obtained for each marker:
Of the transductants selected for arginine,5% are ser⁺ and 30% are amp^R.
Of the transductants selected for serine,3% are arg⁺ and 0% are amp^R.
What is the correct order and relative distance of these three genes on the E.coli chromosome?

Question 37

The viral chromosome of a bacteriophage can never integrate into the host bacterium's chromosome.

Question 38

"Hot spots" are locations in a gene where mutations are found at a relatively high frequency.

Question 39

A bacterial broth culture is diluted by a factor of 100,000,and 0.1 mL of the dilution is spread over the surface of an agar plate.The next day,123 colonies are observed on the plate.What was the concentration of bacteria in the broth?

Question 40

How would you design an experiment to test whether a transduction event occurred between two different bacterial strains?

Question 41

How does a bacteriophage become a transducing phage?

Question 42

Performing a complementation test through cotransduction using mutant phage genomes created by X-ray mutagenesis (mutants a-e),as well as ones created by chemical mutagenesis using EMS (mutants 1-5),you get the following results:
1 2 3 4 5
a - + + - -
b - + - - -
c + + - - +
d + - + + -
e - - + + -
Explain this data.

Question 43

In bacteriophage T4,all rIIA mutants are found to complement all rIIB mutants.However,rIIA mutants fail to complement other rIIA mutants,and rIIB mutants fail to complement other rIIB mutants.Furthermore,mutants with deletions that span both rIIA and rIIB complementation groups do not complement either A or B mutants.What do these data mean,and what do the complementation groups represent?

Question 44

How could you use T2 bacteriophage plaque phenotypes to determine the genetic distance between two genes,h and r,that affect plaque appearance in the phage DNA?

Question 45

How did Seymour Benzer use deletion mapping to construct fine-scale maps of the rII region of the T4 bacteriophage genome?