Genetics Ch.7: Bacterial and Phage Genetics

How many chromosomes do bacteria have

1 circular haploid chromosome

How to score phage phenotypes

1. Coinfect 2. Isolate progeny phage 3. Plate on mixed lawn (few phage)

What characteristics do we look at for bacterial

1. Colony morphology 2. Resistance 3. Auxotrophs

How do you mate phage

1. High concentration of both + small number of bacteria 3. Bacteria are likely to get coinfection 4. Crossover between phages inside host

Arguments for why conjugation isn't caused by mutation

1. Low probability of multiple mutations on the same gene 2. When plated individually, no recombinant

What are the 2 stages of phages

1. Lytic cycle 2. Lysogenic cycle

2 phenotypes for phage genetics

1. Plaque morphology 2. Host strain

Who discovered cis-trans complimentation

Benzer

What does an catabolic pathway for an auxotroph mean

Can't break something down (i.e. can't use galactose as a carbon source)

What is an auxotroph

Can't grow on MV

What does an anabolic pathway for an auxotroph mean

Can't make something

What is the functional definition of the gene

Cistron: smallest unit that shows us cis/trans effect (cis and trans are different)

What did fine structure mapping show us

Colinearity between mutations (on DNA) and proteins - order of mutations matched the order of amino acids changed on its protein

What kind of phage are in generalized transduction

Defective phage

Who worked out the phage cross

Delbrück

What is fine structure mapping

Detecting very rare XO (XO within a gene)

What is mutation mapping

Determining if a mutant is in the same gene or different genes

What is d

Distance in minutes

What happens in generalized transduction

Entire hot genome gets cut into pieces - each daughter phage contains random piece of the host genome

What determines lysogenic or lytic phase

Environmental conditions (bad conditions -> lysogenic phase)

What does F factor code for

Making of sex pilus that connects 2 bacteria together

What is something eukryotes have that prokaryotes dont

Meiosis

What are genes that compliment each other

Mutants that are on different genes (in Cis or Trans) -> produce wildtype

What does failing to compliment mean

Mutations are on the same genes (in trans) - any mutation in the gene makes nonfunctional protein

What does transformation involve

Naked DNA transfer

What would a T2H+ clearing look like

Only kills one strain but not the other (on mixed plate) - turbid plaque

What is the lysogenic cycle

Phage incorporates into host, will lay dormant for some time

What does transduction involve

Phage transfers DNA

What are temperate phages

Phages with 2 stages

Techniques of phage genetics and what it is called

Plate lawn of bacteria, phage will land on it and create a clearing from killing the bacteria called a plaque

What is specialized transduction

Prophage inside host DNA is supposed to cut itself out to get packaged -> sometimes it makes mistake and packages host DNA with it

What are bacteriophage made of

Protein coat surrounded by nucleic acid (RNA or DNA, circular or linear, SS or DS)

Common way to do screen with bacteria and who did it

Replica plating - Lederberg

How does transformation work

Taking DNA up from the environment using special importing protein

What is induction

Temperate phage switches from lysogenic cycle to lytic cycle because of environmental stressers that are going to kill the host first

What does higher cotransduction frequency mean

The closer the genes are together on the chromosome

What is recombination in bacteria and what is not involved

Transfer and XO of DNA - no gametes involved

What is transduction

Transfer of DNA using bacteriophage (phage)

How do Hfr transfer DNA

Transfers host DNA to recipient, F factor is transferred last

Only way to get mutation on the same gene in cis

Very narrow crossover

What was found in terms of likelihood with FSM

XO not completely random - there are hotspots

Cotransduction frequency equation

cd = (1-d/L)^3

How to do fine structure mapping

rII mutants: only grow on strain B. rII+: B or K12. Independently isolated 300 rII mutants and cross them. Coinfect -> progeny -> plate on k12 (only rII+ can grow - selection)

What is the selection example with met- met+ called

suicide selection

What are Hfr strains

High frequency recombinant - F factor is inserted into the chromosome

What is conjugation mapping not good for

High resolution mapping - can get minutes but not seconds

What kind of transfer do bacteria do

Horizontal nonreciprocal transfer (individual to individual)

What is cotransduction

How often both genes are transferred

How would mutations on the same gene be able to compliment

If they are in cis

What causes specialized transduction

Inaccurate cutting of the host - only genes flanking the prophage

Initial discover of transduction

Infect donor cell -> collect daughter phage -> use them to infect recipient cell -> some genes get transferred with the phage (temperate phage mostly)

How do to selection for auxotroph

Inoculate met- and met+ in minimal liquid media with ampicillin -> amp- won't grow so it won't get killed, met+ will try to grow so it will get killed. Then plate all on complete/supplemental media -> only met- will grow because all met+ is dead

How do lytic cycle phage transfer DNA

Insert their N.A into recipient, replicate inside the cell mostly using host machinery, lyse the host, then spread

What does the temperate phage do in the lysogenic cycle with its DNA and what is it called

Inserts its DNA into the hosts chromosome = prophage -> enters dormant phase

How does gene mapping using conjugation work

Interrupted mating: Interrupt mating at different times to see which genes have transferred

Who worked out transduction

Lederberg

Who worked out conjugation

Lederberg and Tatum

What is cotransformation

2 genes transform together - likelihood 2 genes transform together is related to how close they are

What is L typically for phages

2 minutes

Procedure/selection for generalized transduction

2-point cross: Select for 1 gene, score for the other

2 kinds of transduction

1. Specialized transduction 2. Generalized transduction

3 kinds of bacteria genetic transfers

1. Transformation 2. Transduction 3. Conjugation

How does recipient take on transferred host DNA

2 crossovers flanking the genes

What is F factor

A selfish plasmid - mini chromosome

How do select for 1 gene and score for other

After str kills donor (strs) bacteria, take daughter phages from and allow them to infect recipient. Replica plate on media lacking each gene to see which got which genes.

Why is transformation important

For modifying genes, not mapping them

Who discovered transformation

Griffith - avirulent bacteria + heat killed virulent bacteria

How can resistance be different in bacteria

Resistant to a particular drug

Fundamental difference between screen and selection

Selection is killing non-desired phenotypes. Screen you check each colony

What does conjugation involve

Sex pilus

2 types of plaque morphology

Sharp (rapid lysis) or fuzzy edges (slower lysis)

How does F factor transfer

Single strand through the pilus then they both replicate to be DS

What is L

Size of the phage chromosome in minutes

What happened when they plated the two --++ x ++-- on the MV plate

Some ++++ grew at 10^-5