Lecture 7

Question 1

Describe horizontal (lateral) gene transfer

Answer 1

The organism acquires genes directly from another cell and incorporates them into its genome

Question 2

What is horizontal gene transfer responsible for the spread of?

Answer 2

Spread of fitness enhancing traits e.g. antibiotic resistance

Question 3

What is horizontal gene transfer a mechanism for?

Answer 3

Ongoing adaptive evolution

Question 4

What is conjugation?

Answer 4

DNA transferred through cell-cell contact mediated by mobile genetic element e..g plasmid

Question 5

What is transduction?

Answer 5

DNA transfer mediated by a bacteriophage

Question 6

What is transformation?

Answer 6

Uptake of naked DNA into a competent recipient cell

Question 7

Is a whole chromosome transferred in genetic transfer mechanisms? Why?

Answer 7

No, never a whole chromosome only a segment. This is due to a fragile bridge between the genome and where the DNA is moving

Question 8

TRUE or FALSE

Gene transfer is bi-directional

Answer 8

FALSE

Gene transfer is uni-directional

Question 9

Can transferred DNA fragments be replicated autonomously?

Answer 9

No, to be stably inherited by recipient cell they must be recombined into the recipient chromosome

Question 10

Finish the sentence

Following genetic transfer the recipient is ….

Answer 10

Permanently changed

Question 11

Why was E.Coli chosen for study?

Answer 11

• Non-pathogenic
• Rapid Growth
• Simple nutritional requirements
• Supports growth of a range of bacterial viruses

1st bacterium that sexual recombination was discovered in

Question 12

For detection of genetic exchange, what does sensitivity depend on?

Answer 12

The frequency of reversion

Question 13

Why was Lederberg’s approach good?

Answer 13

• Represented 1st use of conditional mutants to select against parental type
• Mutants were double mutants so reversion artefacts were avoided
• Phototrophic recovery technique had good sensitivity

Question 14

What did the U-Tube experiment conclude?

Answer 14

That physical contact is required for genetic recombination

Question 15

What is surface exclusion?

Answer 15

When an F + (male) doesn’t mate with another F + (male)

Question 16

In Conjugative Plasmid Transfer,

What binds following the nick at origin of transfer?

Answer 16

DNA relaxase covalently binds to 5’ prime

Question 17

Give the basic overview of steps for Conjugative Plasmid Transfer

Answer 17

1. Contact between donor and recipient cells, nick occurs
2. Pillus retracts bringing recipient in closer
3. Rolling Circle DNA replication initiates at 3’ OH and proceeds 5’ -> 3’. Mating bridge is formed.
4. DNA replication pushes ssDNA into recipient cell
5. Lagging strand DNA replicated in recipient converting ssDNA -> dsDNA
6. Following plasmid replication, old and new origins of transfer collide and the sites are separated
7. Mating complex collapses, two F+ donor cells are now present