Chapter 6

Question 1

what are 6 features that make bacteria useful to geneticists?

Answer 1

1. gene simplicity: fewer genes and fewer bases than other organisms
2. uncomplicated genotypes: mutations can be observed directly because there is one copy of each gene
3. rapid generation times: bacterial generation time can be measured in minutes
4. large numbers of progeny: enormous numbers of progeny allow detection of rare events
5. ease of propagation: bacterial culture is easy and inexpensive and takes up very little space
6. numerous heritable differences: mutants are easily created, identified, isolated, and manipulated for study

Question 2

what are the 3 processes of genetic transfer?

Answer 2

1. conjugation
2. transformation
3. transduction

Question 3

what is conjugation?

Answer 3

the transfer of replicated DNA-plasmid transfer-from a donor to a recipient

Question 4

what is transformation?

Answer 4

the uptake of DNA from the environment

Question 5

what is transduction?

Answer 5

the transfer of DNA from one bacterium to another by a viral vector

Question 6

characteristics of genomes in bacteria?

Answer 6

-most have singular, circular chromosome
-many genes are arranged in operons

Question 7

what are operons?

Answer 7

groups of genes that are transcribed together because they have interacting functions

Question 8

what are characteristics of plasmids?

Answer 8

-small double-stranded circular DNA molecules containing non-essential genes
-considerably smaller than bacterial chromosomes
-usually appear as multiple copies when present in most bacteria
-many kinds of naturally occurring plasmids are found in bacteria

Question 9

What are 2 types of plasmids?

Answer 9

1. the F (fertility) plasmid
2. the R (resistance plasmid)

Question 10

what is the F plasmid?

Answer 10

contains genes that promote its own transfer from donors to recipients

Question 11

what is the R plasmid?

Answer 11

carries antibiotic resistance genes that can be transferred to recipient cells

Question 12

Characteristics of plasmid replication?

Answer 12

Many plasmids can replicate independently of the bacterial chromosome so that the number of plasmids per cell can increase rapidly
* These are called “high-copy-number” plasmids and the actual number—50 or more—per cell is variable
* Low-copy-number plasmids are present in one or two copies per bacterial cell and usually cannot replicate independently of the bacterial chromosome

Question 13

What does bacterial conjugation require?

Answer 13

a fertility factor

Question 14

What does the F plasmid allow to happen?

Answer 14

required in order for bacteria to be able to transfer genetic material by physically linking together and transferring DNA,

Question 15

What occurs in bacterial conjugation?

Answer 15

F plasmid uses DNA replication machinery of the cell and inhibits contact with other F+ cells
-the genetic transfer is one way-Donor F+ to recipient F-

Question 16

How is the transfer of Hfr chromosomes similar/different to transferring F factor

Answer 16

The whole chromosome is not transferred as conjugation does not last long enough

Recombination has to occur before
degradation of the linear DNA

Question 17

What can the transfer of Hfr chromosome introduce into the recipient?

Answer 17

new alleles due to the transfer of only a portion of the F plasmid so the recipient is not F-
-needs 2 crossover events to occur to have this portion of F plasmid inserted into the recipient genome

Question 18

Can the F factor only insert at one IS site?

Answer 18

no, it can insert at several different IS sites at multiple places in the bacterial chromosome in either direction

Question 19

what can hfr strains be used to determine over larger chromosomal distances?

Answer 19

gene order–>can produce a consolidated map

Question 20

What 4-step process occurs during transformation?

Answer 20

1. donor DNA binds at the receptor site. one strand is degraded as it enters the recipient cell
2. the transforming strand pairs with the homologous region of the recipient chromosome
3. the transforming strand displaces a recipient strand, forming complementary heteroduplex DNA. The excess strand degrades
4. DNA replication and cell division produce one transformant and one nontransformant

Question 21

what precedes transformation?

Answer 21

lysis, which is where the cell dies and releases DNA into the environment–>this become the “donor DNA”

Question 22

what is cotransformation?

Answer 22

The closer genes are, the more likely
they will transform a recipient together

Question 23

what is bacteriophage?

Answer 23

-viruses that infect and parasitize bacteria

Question 24

what occurs during transduction?

Answer 24

phage enters host cell, synthesizes new proteins and replicates chromosome befroe host chromosome degrades, as the host chromosome degrades the phages assemble within the cell, there is lysis of the host cell, and then the phages are free to infect other cells