Genetics I Mechanisms of Diversity

Question 1

Bacterial chromosome characteristics

Answer 1

• Circular dsDNA
• Approx 5000KB
• Approx 1.33 mm long (compared to 990 mm chromosomal length)
• Structure maintained by polyamines
• May contain extrachromosomal elements such as plasmids or bacteriophages

Question 2

Plasmid

Answer 2

Small genetic element, replicates independently of chromosome
Usually circular dsDNA, some can integrate

Question 3

Bacteriophage

Answer 3

Bacterial virus with a protein coat and genomic DNA or RNA,

two infection stages: lytic or lysogenic

Question 4

Transposon

Answer 4

Mobile genetic element, with an insertion sequence that has inverted repeats at both ends. Complex transposons can carry additional information such as anti-infective resistance, may sometimes insert into genes and inactivate them.

Question 5

Conjugation

Answer 5

Mating between two cells, one with conjugative plasmid (F) which has genes for its own transfer included sex pilus encoding and DNA synthesis initiation at plasmid OriT.

Question 6

Transformation

Answer 6

Bacterial cells take up fragments of naked DNA and incorporate into their own genome.

Question 7

Transduction

Answer 7

Transfer mediated by bacteriophages which pick up DNA fragments, bacteriophages package them into particles and deliver them to bacterial cell via infection.

Generalized transduction (accidental packing of host DNA into capsid) may also occur.

Specialized transduction: transfer of particular genes