Deck 6: Genetic Analysis and Mapping in Bacteria and Bacteriophage

Question 1

In a partially diploid F′ exconjugant,there are two alleles for lac (1 and 2)and two alleles for his (3 and 4).The phenotype of this cell is identical to a lac 1 his 4 cell.What is the best interpretation?

A)Lac 1 and 2 and his 3 and 4 share only lac 1 and his 4 phenotypes.
B)Lac 1 complements lac 2 and his 3 complements his 4.
C)Lac 1 and his 4 are dominant.
D)Lac 1 and his 4 are wild types.
E)Lac 1 shows its phenotype only if his 4 is also present.

Answer 1

C

Question 2

An F′ donor includes F DNA plus a segment of bacterial chromosome DNA.If conjugation is interrupted before the entire F′ chromosome transfers,what could be the expected consequences?

A)integration of some but not all F′ genes into the recipient's chromosome
B)a smaller F′ plasmid than had been present in the donor
C)failure of the F′ strand to circularize in the recipient
D)change of the recipient from F⁻ to F⁺
E)formation of a recipient that is a stable partial diploid

Answer 2

C

Question 3

In generalized transduction,a phage introduces a segment of donor DNA into the recipient cell.This is followed by recombination of the donor fragment with the recipient chromosome.Which of the following must occur?

A)circularization of the donor fragment before recombination
B)a pair (or even number)of crossovers between the donor segment and the recipient
C)degradation of one of the two strands of phage genome
D)replication of the donor segment before recombination
E)a single crossover between the donor segment and the recipient chromosome

Answer 3

B

Question 4

A competent Hemophilus strain is individually transformed by three genes (a,b,and c)at a rate of 0.002% each.However,cotransformation frequencies for each pair are as follows: a and b 0.38 %
A and c 0.72%
B and c 0.19%
What is the correct conclusion from this data?

A)Genes b and c are farthest apart.
B)Gene order is c,b,a.
C)Cotransformation of b and c is so frequent,they must be one gene.
D)Gene a is closer to b than to c.
E)Genes a and c are farthest apart.

Question 5

In five Hfr strains,each of which was used to build a time-of-entry map,the genes entered the recipient cells as follows: Strain 1: S L A C T F
Strain 2: N P F T C A
Strain 3: T F P N U Y
Strain 4: S H Y U N P
Strain 5: U N P F T C
Which of the following represents a correct compilation of these results?

A)S L A C T F P N H C U
B)N P F T S L A C H U T
C)T C A L S P N U Y H
D)U N P F T C A L S T F
E)S L A C T F P N U Y H

Question 6

Refer to this text to answer the following questions.
Bacterial gene transfer is also used in the lab to introduce genes into organisms of different species,genera,phyla,or even kingdoms or domains.A major example is the use of a Ti plasmid of the soil bacterium Agrobacterium tumefaciens to transfer genes into dicotyledonous plants.The bacterium infects the plant root in the soil and transfers some of the Ti plasmid genes (T DNA)into the plant nucleus.Recombination may occur,and T DNA expression is controlled by plant compounds generated in response to wounding and infection.
This method can be used to introduce a gene for an antigenic protein into an edible plant,such as a potato,to produce an edible vaccine (e.g.,for cholera).What has to be made a part of the Ti plasmid?

A)a gene for cholera resistance
B)a gene for a subunit of cholera toxin,including its regulatory elements
C)a gene for that part of the human immune system that neutralizes cholera
D)a molecule of anti-cholera antibody
E)a polypeptide that can attach the T DNA to plant DNA

Question 7

A large region of the F plasmid (~33 kb)is called the transfer region (tra)and contains about 40 genes necessary for conjugation.The gene traA codes for the protein pilin that is polymerized to form a pilus,using a number of other tra genes.The pilus is a hollow cylinder whose units disassemble once contact is made in order to "reel in" the recipient cell.What other functions of the tra genes are required for transfer?

A)DNA unwinding,and restriction of contact with F⁺ cells
B)DNA replication enzymes
C)resistance to phage infection
D)integration of F genes into the recipient's chromosome
E)integration of F genes into the recipient's plasmid

Question 8

To integrate an F plasmid's genes into a host chromosome,there must be DNA recombination at homologous regions on the two circular strands.What is the minimum number of such crossover events needed for integration?

A)1
B)2
C)3
D)4
E)8

Question 9

This graph shows the results of plating the cultures of each blender.What is the correct order of the genes on this chromosome?

A)a b c d e
B)a c e b d
C)b e c a (d is unknown)
D)d a c e b
E)b e c a d

Question 10

Why does conjugation with an Hfr donor result in a much higher rate of gene transfer than conjugation with an F⁺ donor?

A)An F⁺ donor makes fewer pili.
B)An F⁺ donor's T strand is slow to reach the pilus.
C)The Hfr donor transfers genes from the chromosome and not the plasmid.
D)The Hfr donor segment must undergo recombination in the recipient.
E)The F⁺ donor segment must undergo recombination in the recipient.

Question 11

Which of the following allows the compilation of time-of-entry maps?

A)the use of many replicates of each experiment
B)the use of appropriate controls repeatedly
C)the fact that gene entry can proceed in either direction
D)the observation that Hfr genes recombine so efficiently
E)the recognition of phenotype interaction

Question 12

Refer to this text to answer the following questions.
Bacterial gene transfer is also used in the lab to introduce genes into organisms of different species,genera,phyla,or even kingdoms or domains.A major example is the use of a Ti plasmid of the soil bacterium Agrobacterium tumefaciens to transfer genes into dicotyledonous plants.The bacterium infects the plant root in the soil and transfers some of the Ti plasmid genes (T DNA)into the plant nucleus.Recombination may occur,and T DNA expression is controlled by plant compounds generated in response to wounding and infection.
Assuming you have appropriately engineered the Ti plasmid to carry the gene in question,how could you best and most safely test whether your potatoes are now working as a vaccine?

A)Feed the engineered potato to a population at high risk for cholera.
B)Cook the potatoes to denature the toxin and feed them to mice susceptible to cholera.
C)Feed pieces of raw potato to susceptible mice and test them for antibodies.
D)Emulsify the potatoes in a liquid that can be injected into experimental animals.

Question 13

Refer to this text to answer the following questions.
To map genes of a bacterial strain,conjugation must be interrupted at given times.Suppose you have Hfr cells of genotype a⁺ᵇ⁺ᶜ⁺ᵈ⁺ᵉ⁺ˢᵗʳᴿ and F⁼ cells of genotype a⁻ᵇ⁻ᶜ⁻ᵈ⁻ᵉ⁻ˢᵗʳˢ and you combine these two cultures in liquid medium in four blenders at time 0.After intervals of 3,6,9,and 12 minutes,you turn on successive blenders.
The resulting cultures were then plated on medium containing streptomycin.Why?

A)to eliminate non-conjugating Hfr cells
B)to eliminate all non-conjugated cells
C)to eliminate non-conjugated F⁻ cells
D)to selectively eliminate cells that have taken in F⁺ genes

Question 14

In an imagined transduction experiment with alleles a⁺,b⁺,and c⁺,a⁺ alone was transduced into an auxotroph 1400 times,b⁺ alone 1200 times,and c⁺ alone 970 times.Genes a⁺ and b⁺ were both found 10 times,b⁺ and c⁺ 2 times,and a⁺ and c⁺ one time.What can you conclude?

A)Cotransduction is too infrequent to be used to map genes.
B)Genes a and c cotransduce only accidentally.
C)Genes a and b are more closely linked than a and c or b and c.
D)Genes a and c are found together only if double crossovers have occurred.
E)Transduction of gene c is very rare.

Question 15

Refer to this text to answer the following questions.
To map genes of a bacterial strain,conjugation must be interrupted at given times.Suppose you have Hfr cells of genotype a⁺ᵇ⁺ᶜ⁺ᵈ⁺ᵉ⁺ˢᵗʳᴿ and F⁼ cells of genotype a⁻ᵇ⁻ᶜ⁻ᵈ⁻ᵉ⁻ˢᵗʳˢ and you combine these two cultures in liquid medium in four blenders at time 0.After intervals of 3,6,9,and 12 minutes,you turn on successive blenders.
What role does the blender play in the experiment?

A)serves as a culture container only
B)acts as a mechanism to bring cells into contact
C)speeds up molecular movement of DNA
D)shears the sex pili of conjugants
E)hastens conjugation events

Question 16

Refer to this text to answer the following questions.
Bacterial gene transfer is also used in the lab to introduce genes into organisms of different species,genera,phyla,or even kingdoms or domains.A major example is the use of a Ti plasmid of the soil bacterium Agrobacterium tumefaciens to transfer genes into dicotyledonous plants.The bacterium infects the plant root in the soil and transfers some of the Ti plasmid genes (T DNA)into the plant nucleus.Recombination may occur,and T DNA expression is controlled by plant compounds generated in response to wounding and infection.
The T DNA is generated when there is a nick that creates a primer for replication,followed by transfer of a single-stranded DNA piece that converts to a double-stranded piece in the plant nucleus.Which of these processes is Ti plasmid transfer most like?

A)conjugation
B)generalized transduction
C)specialized transduction
D)transformation

Question 17

When F⁺ conjugation occurs successfully,only one copy of the F plasmid single-stranded DNA is transferred.What else must minimally occur?

A)circularization of the recipient's new DNA
B)circularization plus replication of the new recipient DNA
C)stopping the rolling circle replication after one copy length,circularization,and replication
D)continuation of rolling circle replication in the donor cell and replication in the recipient cell
E)rolling circle replication in the recipient cell

Question 18

When F⁺ conjugation occurs successfully,only one copy of the F plasmid single-stranded DNA is transferred.What else must minimally occur?

A)circularization of the recipient's new DNA
B)circularization plus replication of the new recipient DNA
C)stopping the rolling circle replication after one copy length,circularization,and replication
D)continuation of rolling circle replication in the donor cell and replication in the recipient cell
E)rolling circle replication in the recipient cell

Question 19

In his analysis of rII in phage,Benzer assayed complementation.Suppose you try your hand at this with several mutants and get the following results (+ = complementation): 42 and 62 +
42 and 83 -
62 and 63 -
62 and 74 +
42 and 74 -
42 and 75 +
62 and 75 -
Mutation 42 has previously been shown to be in a different gene than mutation 62.What can you conclude?

A)Mutations 42 and 75 are in the same gene.
B)Mutations 62 and 74 are in the same gene.
C)Mutations 62,63,and 74 are in the same gene.
D)Mutations 42 and 74 are in the same gene.
E)Mutation 63 is in a gene with neither 62 nor 42.

Question 20

In phi X 174 phage,whose genome is a single-stranded,circular,DNA known as the - strand,replication occurs by the rolling circle method.In which order must the events of replication occur?

A)nicking of the - strand,binding of relaxase protein to the 5′ end,DNA synthesis of a + strand,separation of + from - strands,circularization of both strands
B)synthesis of a + strand,nicking at the origin,binding of protein to the 5′ end,DNA synthesis,displacement of the + strand when replication passes the origin,circularization of the + strand
C)synthesis of a + strand,nicking of both strands to separate them,recircularization of both strands
D)binding of a protein at the origin of the - strand,synthesis of a + strand,release of the + strand

Question 21

What characterizes a bacterial cell that can undergo transformation?

Question 22

What is the difference between F⁺ and F⁻ bacteria?

Question 23

In a bacterial cross of an Hfr donor a⁺b⁺ with a recipient F⁻ a⁻b⁻,what would be a possible recombinant?

Question 24

If conjugation occurs with an F′ donor,how will the recipient be characterized genetically?

Question 25

What distinguishes generalized versus specialized transduction?

Question 26

Jacob and colleagues developed a bacterial linkage map based on time.What kind of recombination was used?

Question 27

What is the role of the relaxosome in conjugation?

Question 28

In a conjugation experiment,the Hfr donor is thr⁺,leu⁺,his⁺,str.The recipient is thr⁻,leu⁻,and his⁻ strˢ.Why would you use medium containing streptomycin to analyze your results?

Question 29

Which form of bacterial recombination requires no vector?

Question 30

In Hfr transfer,what happens to linear DNA that does not recombine with the host chromosome?

Question 31

In an E.coli conjugation experiment,the donor cell is found to be thr⁺,leu⁺,his⁺,and the F⁻ cell is thr⁻,leu⁻,and his⁻.When the mating is interrupted after 10 minutes and the recipients are plated,they are found to be leu⁺ and his⁺ but thr⁻.What can you conclude?

Question 32

All three types of bacterial recombination share one characteristic.What is it?

Question 33

In a transduction experiment,what would constitute evidence of linkage?

Question 34

If you count 73 plaques on a bacterial plate when you had added 0.1 ml of a 10⁻⁴ dilution of phage,what was the initial concentration of the (undiluted)phage?

Question 35

Describe two features of a plasmid.

Question 36

Name the three usual phases of bacterial growth in a liquid medium.

Question 37

One kind of plasmid in bacteria is called an R plasmid.What kinds of genes are typical of such plasmids?

Question 38

Name the two cycles in which bacteriophages act when they infect bacteria.

Question 39

Refer to this text to answer the following questions.
Bacterial gene transfer is also used in the lab to introduce genes into organisms of different species,genera,phyla,or even kingdoms or domains.A major example is the use of a Ti plasmid of the soil bacterium Agrobacterium tumefaciens to transfer genes into dicotyledonous plants.The bacterium infects the plant root in the soil and transfers some of the Ti plasmid genes (T DNA)into the plant nucleus.Recombination may occur,and T DNA expression is controlled by plant compounds generated in response to wounding and infection.
Benzer's analysis of phage genomes included deletion mapping.Since recombination could not occur in the area of a deletion,an infection by two phage strains,one of which has a deletion and the other a point mutation,which results in no wild-type recombinants being produced indicates ________?

A)that the deletion includes the position of the point mutation in the same gene
B)that the deletion includes the position of the point mutation in a different gene
C)that the point mutation is dominant
D)that the point mutation is recessive
E)the distance between the two types of mutation

Question 40

In conjugation,as the 5′ end of the T strand begins to move across the pilus,what form of replication occurs in the donor cell?

Question 41

What is meant by a mutation that Benzer referred to as nonrevertible?

Question 42

Prototrophs are bacteria that can grow on ________ medium.

Question 43

Once a phage genome has become part of the host chromosome,it is called a ________.

Question 44

Which,if any,characteristics of bacterial gene transfer is/are useful in analyzing eukaryotic gene transfer?

Question 45

Seymour Benzer's fine structure studies of genomes used mutations found in specific regions of what kind of genome?

Question 46

Conjugation,transduction,and transformation all occur in nature.Which do you expect would more likely account for the acquisition of the genes for resistance to an antibiotic? Why? Which do you think would best account for the acquisition of genes from one bacterial species by another of a different genus? Why?

Question 47

How are selective media used in studying bacterial recombination?

Question 48

Some bacteriophages can be either lytic or lysogenic.These are called ________ phages.

Question 49

When a soil bacterium infects a plant root and introduces its Ti plasmid,how does this affect both the infectious bacterium and the plant?

Question 50

Arabinose sugar is used by ara⁺ bacteria but cannot be used by ara⁻ mutants.When both ara3 and ara5 mutants are introduced into the same recipient via a vector,and the recipients still cannot use arabinose,what can you conclude?

Question 51

Explain when,why,and how recombination in bacteria is like crossing over in diploid cells.