Q: In a serial dilution experiment, you plate 1 mL of a $$10^{-6}$$ dilution and count 50 colonies. What is the concentration of cells in the original culture?

$$5 \times 10$$^{7}$$ cells/mL$

Question 1

Which of the following best describes the genetic material of most bacteria and viruses, and why are mutations in these organisms directly expressed?

Accepted Answer

They are haploid, so all mutations are directly expressed without masking.

Question 2

A bacterial strain that can grow on minimal media by synthesizing all essential organic compounds is called a:

Accepted Answer

Prototroph

Question 3

In a serial dilution experiment, you plate 1 mL of a $$10^{-6}$$ dilution and count 50 colonies. What is the concentration of cells in the original culture?

Accepted Answer

$$5 	imes 10$$^{7}$$ cells/mL$

Question 4

Which process in bacteria involves the replacement of one or more genes present in the chromosome of one cell with those from a genetically distinct cell, analogous to crossing over in eukaryotes?

Accepted Answer

Genetic recombination

Question 5

What is the main difference between vertical and horizontal gene transfer in bacteria?

Accepted Answer

Vertical transfer occurs between members of the same species; horizontal transfer occurs between unrelated cells or species.

Question 6

During bacterial conjugation, which cells serve as donors of genetic material, and what factor do they possess?

Accepted Answer

F$$^+$$ cells; they possess the F factor.

Question 7

Why is physical contact between bacterial cells necessary for conjugation to occur?

Accepted Answer

It allows the transfer of plasmids through the F pilus.

Question 8

Which of the following statements about plasmids is correct?

Accepted Answer

Plasmids are double-stranded closed circles of DNA that use the host's replication enzymes.

Question 9

R plasmids in bacteria have two main components. What are they, and what is their function?

Accepted Answer

RTF (Resistance Transfer Factor) for transfer and R-determinants for antibiotic resistance.

Question 10

Col plasmids encode colicins, which are highly toxic proteins. What is the effect of colicins on bacterial populations?

Accepted Answer

They kill bacterial strains that do not harbor the same plasmid.

Question 11

Which process allows small pieces of extracellular DNA to be taken up by a living bacterial cell, leading to stable genetic change?

Accepted Answer

Transformation

Question 12

If two loci cotransform frequently in a transformation experiment, what does this indicate about their genetic relationship?

Accepted Answer

They are closely linked.

Question 13

What physiological state must a bacterial cell be in to take up DNA during transformation?

Accepted Answer

Competence

Question 14

In transformation studies, why can genes close together on the bacterial chromosome be cotransformed?

Accepted Answer

Because the DNA segment taken up is large enough to carry multiple linked genes.

Question 15

Which process is responsible for bacterial recombination mediated by bacteriophages, as discovered in the Lederberg–Zinder experiment?

Accepted Answer

Transduction

Question 16

During generalized transduction, what is randomly packaged in the phage particle and transferred to the recipient host?

Accepted Answer

Bacterial DNA

Question 17

Transduction can be used in linkage and mapping studies of bacterial chromosomes. What is the relationship between cotransduction frequency and gene linkage?

Accepted Answer

The closer linked genes are, the greater the frequency of cotransduction.

Question 18

When live Streptococcus pneumoniae cells from rough colonies are mixed with dead cells from smooth colonies, smooth colonies can be isolated. This is most likely due to:

Accepted Answer

Transformation

Question 19

A multi-step scenario: You are studying two auxotrophic E. coli strains, each unable to grow on minimal media. After mixing them, you observe growth on minimal media. Which process most likely occurred, and what is the genetic outcome?

Accepted Answer

Conjugation; genetic recombination produced prototrophs.

Question 20

Which equation would you use to calculate the original concentration of bacteria in a serial dilution experiment, given the number of colonies and the dilution factor?

Accepted Answer

$$	ext{Original concentration} = 	ext{Number of colonies} 	imes 	ext{Dilution factor}$$

Ch 8 Genetic Analysis and Mapping in Bacteria and Bacteriophages

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