Deck 25: Genetics: an Introduction

Question 1

The E. coli chromosome is

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

Answer 1

D

Question 2

Which type of genetic exchange in bacteria involves a plasmid?

A) Conjugation
B) Transduction
C) Transformation
D) Both A and C
E) All of the above

Answer 2

D

Question 3

Who first observed bacterial transformation in 1928?

A) Oswald Avery
B) Linus Pauling
C) Edward Tatum
D) James D. Watson
E) Frederick Griffith

Answer 3

E

Question 4

Cotransductants can be detected when the transduced genes are

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

Question 5

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

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

Question 6

The transformation frequencies for genes A and B are each 10-3. The frequency of cotransformation for these two genes is also 10-3. Therefore these genes are probably

A) on two different chromosomes.
B) on two separate plasmids inside the cell.
C) very close to each other on the chromosome.
D) far apart from each other on the chromosome.
E) Both B and 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) auxisome.
C) episome.
D) elaiosome.
E) perisome.

Question 8

The virulent T2 bacteriophage life cycle is characterized as

A) a lysogenic pathway only
B) lytic and lysogenic cycles
C) a prophage pathway
D) a lytic cycle only
E) none of the above.

Question 9

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

Question 10

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 without. The transformed cells would grow on

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

Question 11

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

Question 12

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

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

Question 13

What did Lederberg and Tatum's 1946 experiment show?

A) That genetic exchange between bacterial cells is a bidirectional process
B) That viruses are required for genetic exchange between bacterial cells
C) That sexual recombination can occur between bacterial cells
D) That bacterial cells can be made to uptake bits of DNA from the environment
E) That genetic recombination in bacteria occurs at a very high rate

Question 14

Homoallelic mutations affect the same

A) species.
B) chromosome.
C) gene.
D) allele.
E) nucleotide pair.

Question 15

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

Question 16

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) Both B and C
E) is replaced by a piece of bacterial DNA when packaged inside phage progeny.

Question 17

To grow on artificial medium, prototrophic bacteria require

A) amino acid supplements.
B) vitamin supplements.
C) sunlight.
D) all of the above.
E) none of the above.

Question 18

E. coli strains that are Hfr

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

Question 19

Which of the following can make competent bacterial cells?

A) Treating the cells chemically
B) Anything that makes the cell membrane more permeable to DNA
C) Exposing cells to a strong electric field
D) Allowing the culture to enter stationary phase growth
E) All but D

Question 20

Cotransductant bacteria can occur if

A) a bacterial cell picks up two fragments of DNA from the environment, each with a different gene.
B) 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.
C) double-crossover occurs between prophage DNA and the bacterial chromosome.
D) two genes are introduced into the same bacterium by simultaneous infection with two different phages.
E) Both C and D

Question 21

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

Question 22

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

Question 23

What are temperate bacteriophages?

Question 24

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 25

Bacillus subtilis is an example of a bacteria that must be engineered to undergo genetic transformation.

Question 26

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 27

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

Question 28

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

Question 29

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

Question 30

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 31

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 32

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

Question 33

How does a bacteriophage become a transducing phage?

Question 34

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

Question 35

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

Question 36

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

Question 37

All the cells in a bacterial colony are genetically identical.

Question 38

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

Question 39

Interrupted mating experiments were done with four different Hfr bacterial strains H, 1, 2, and 3 to determine the order of integrated F factor genes in the recipient. From the gene maps of the four strains given here, the following alignment was made: Order of gene transfer: H thr-pro-lac-pur-gal 1 his-gly-thi-thr 2 his-gly-thi-thr-pro-lac 3 pro-lac-pur-gal-his-gly Alignment of genes: H thr-pro-lac-pur-gal 1 his-gly-thi- thr 2 his-gly-thi-thr- pro-lac 3 pro-lac-pur-gal-his-gly What does this alignment imply about the structure of the Hfr bacterial chromosome?

Question 40

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 41

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?