Genetics Ch. 9 [II]

discovery of generalized transduction

- set up a U tube and noticed that prototrophs were formed so it was NOT contact dependent - the "factor" (temperate phage) moved through the filter and moved genes

merodiploid

-partially diploid - caused by F-duction

co-transduction of genes

1. close together on the chromosome (1 infection) 2. carried by 2 different phages (simultaneous infection)

Steps of Generalized transduction

1. phage enters cell and breaks bacterial DNA 2. assembly of WT and transducing phages (w/ bacterial genes in head) 3. lysis 4. infection of recipient bacterium with transducing phage 5. genetic exchange of donor gene with recipient gene by DCO 6. stable transduced bacterium produced by recombination 7. linear fragments degraded

interrupted-mating

2 strains (use one that you know is sensitive to something -HfrH- and one you know is resistant to something...in the end, you only want the F⁻ - resistant one) mixed together, allowed to conjugate 2. bacteria grown under diff. media conditions to determine phenotype 3. about 100 min to transfer all genes 4. map the genes (distance measured in minutes)

F'

F factor can be removed from bacteria chromosome and when doing so, takes part of the chromosome with it-- called F'

F-duction

F' factor- F'(lac) - 2 circles of DNA- making the bacteria partially diploid (merodiploid)

Hfr strain

High-frequency recombination strain of E. coli - The F factor can integrate into the bacteria chromosome forming an Hfr strain - then, when Hfr bacteria conjugate with F⁻ bacteria, part of the bacterial chromosome will be transferred (can be used to map bacterial chromosome

tranduction

a process by which bacteriophages (phage vectors) transfer genes from one bacterium (donor) to another (recipient) - may undergo genetic recomb w/homologous region of recipient's chromosome

bacteriophage (T2)

can carry genes from former host to new host (at most 1%)

F factor

conjugative plasmid that can copy itself into an F⁻ bacteria via conjugation pilus (that it forms)

generalized vs. specialized transduction

generalized: any genes can be transferred between bacteria specialized: only specific genes can be transferred

complete media

in addition to minimal media ingredients, includes vitamins, AA, etc.

Lysogenic vs. Lytic

lysogenic: phage embeds its DNA into the host chromosome, replicates many times, excises its DNA and joins lytic lytic: phage inserts its DNA into host cell and replicates only its DNA and then makes translates itself and bursts cell open

transductants

recombinant recipient

mixing of complementary auxotrophic and phototrophic bacteria

showed that genes are not transferred through the media, but that they are contact dependent

phototrophs

strains that do not need nutritional supplementation - ex: bacteria are able to make leucine by itself rather than having it on the plate

auxotrophs

strains unable to synthesize essential nutrients, need nutritional supplementation - may be caused by a mutation preventing the production of something

how to map transduction data

the higher the %, the closer they are together

minimal media

the nutrients required for the growth of WT bacteria - carbon source, salts, trace elements

transformation

transfer of extracellular DNA into cells - DNA is taken up and recombines with bacterial chromosome (heteroduplex formation) - the more tightly linked the genes, the more likely they will be transformed together - can use to map genes (similar to radiation hybrid technique for humans)

phage

virus that can infect bacteria