Genetics Exam 2

Front 1

Fluctuation test by Lure and Delbruck

Back 1

spontaneous mutation is the primary source of genetic variation in bacteria.

Front 2

Prototrophs

Back 2

can synthesize all essential organic compounds for growth from a "minimal medium" (single carbon and nitrogen sources and inorganic ions)

Front 3

Auxotrophs

Back 3

mutation results in loss of the ability to make at least one essential organic component

Front 4

Genetic Recombination in Bacteria

Back 4

Conjugation
Transformation
Transduction
*Sources of genetic variation
*Genetic maps (order of genes on chromosome)

Front 5

Lederberg and Tatum

Back 5

Bacteria undergo a "parasexual" process
Genetic material from one bacterium is transferred to and recombine with that of another.
*Conjugation*
Mixed 2 multiple auxotrophs and obtained prototrophs

Front 6

Davis U Tube Experiment

Back 6

Showed that physical contact b/w two cells is required for genetic recombination

Front 7

Conjugation: F-factor

Back 7

F-factor is mobile: recipient cells always become F+ after conjugation
F-factor is a large plasmid: Circular, double stranded, About 100,000 base pairs, Has 19 genes involved in formation of the pilus and conjugatoin

Front 8

F-factor mechanisms

Back 8

When F-factor present, the cell can form a pilus and has the potential to serve as a donor of genetic material
A single strand of the F-factor plasmid is transferred during conjugation: both strands are replicated as the plasmid unwinds and DNA is transferred to the recipient cell
In F+ x F- conjugation, none of the bacterial chromosome is transferred.

Front 9

Hfh (High frequency Recombination) Bacteria

Back 9

Donor bacteria trains that undergo recombination at a rate much higher than F+ cells
Hfr cells are a special class of F+ cells
Originate by a rare crossover event in which the F factor integrates into the bacterial chromosome.
The F factor now replicates w/the host chromosome instead of independently.
F factor is integrated into the donors chromosome, and chromosomal genes can be transferred during conjugation.
F factor is transferred last (if at all).

Front 10

Genetic Mapping in Hfr strains

Back 10

"interrupted mating technique: certain genes transferred before others, always in a certain order
Time between transfer could be used as a measure of "distance" of the genes from one another.
Used to create the first "genetic map" w/minutes corresponding to "map units" in eukaryotes.
Diff. Hfr strains have F factor integrated as diff. sites: these serve as origin of transfer.

Front 11

rec genes

Back 11

mutations in the rec genes decrease the frequency of recombination of a F+ plasmid by 100-1000 fold.
recA, recB, recC, and recD

Front 12

R plasmids

Back 12

Small circular double stranded DNA molecules
Distinct from the genomic DNA
R plasmids contain one or more resistance factors such as antibiotic resistance genes.
Transposons often allow movement of the r genes.

Front 13

Bacterial Transformation

Back 13

Mechanism for uptake of DNA into a bacterial cell, can result in recombination.
The DNA recombines with a homologous region in the recipients chromosome: leads to stable exchange of genetic information.

Front 14

Transformation & Genetic Mapping

Back 14

Only if the recombined DNA produces a different phenotype than the original phenotype of the recipient strain.

Front 15

Genetic Analysis of Bacteriophage

Back 15

Transduction: bacterial recombination mediated by bacteriophage
Lederberg-Zinder Experiment: Used a Davis-U-tube, found that recombination b/w two strains of Salmonella occurred w/out the cell determined to be a phage

Front 16

lytic

Back 16

bacteriophage infects the cell, replicates, and lyses the cell

Front 17

lysogenic

Back 17

bacteriophage infects the cell, but the phage DNA integrates in the host cell genome
No new phage are produced
phage DNA replicates with the host cell DNA, no cell lysis

Front 18

Cell Stress Conditions & Bacteriophage

Back 18

Phage DNA is excised from the host genome
Phage reproduction is initiated
Bacteria is lysed to release new phage

Front 19

Transduction by Bacteriophage

Back 19

Excision of prophage DNA from bacterial genome is imprecise and can take bacterial DNA as well
This DNA is packaged into the phage head and can then integrate into the chromosome of a newly infected bacteria
Phage lysis of bacteria causes the host bacteria DNA to be degraded: this DNA can then be packaged into the viral head.

Front 20

Abortive Transduction

Back 20

a phage with bacterial DNA infects a cell but the DNA does not recombine into the new hosts chromosome

Front 21

Complete Transduction

Back 21

when the bacterial DNA recombine with its homologous region of the bacterial chromosome.

Front 22

Cotransduction

Back 22

Genes that are closely linked on the bacterial chromosome can be simultaneously transduced

Front 23

Transduction mapping

Back 23

used to determine gene order
Similar to mapping using the interrupted mating technique
Genes that cotransduce are closely linked