Genetics of Bacteria and Viruses.

Prokaryote Circular genome

DNA that forms a closed loop and has no ends

Plasmids

Circular DNA molecules that can replicate independently of the main chromosomes of bacteria-- Essentially smaller pieces of DNA.

Bacteria transformation

"naked" DNA enters bacteria cell from environment and become incorporated in its genomic DNA

Bacteria transduction

when a virus relocates bacterial DNA from one bacteria to another via lysogenic cycle

Conjugation

In bacteria, the direct transfer of DNA between two cells that are temporarily joined.

Two ways bacteria conjugate

Plasmid transfer from one bacteria to another, or partial genome transfer from one bacteria to another.

Vertical transmission

parent to offspring transmission

Horizontal transmission

Transmission of genetic information between individuals in the same generation, who may be unrelated.

Joshua Lederberg and Edward Tatum

Discovered that DNA can be transferred from one bacterium to another (conjugation)

Auxotrophie

an organism that cannot make a specific organic compound (like an amino acid or vitamin) that it needs to grow.

Lederberg and Tatum experiment

Used two triple auxotrophic e. coli strains with different nutrient requirements and established three separate bacterial cultures growing in complete medium. Moved culture 1 into a minimal medium, and it did not grow. Moved culture 2 into a minimal medium, and it did not grow. Moved culture 3 (which was a combination of both strands) into a minimal medium, and phototrophic cells grew. Denied it could be a reverse mutations because it's very unlikely that all genes reverted (low chances) and, if there had been any reversion, cultures 1 and/or 2 would have also grown. Thus, they concluded that the strains transferred genetic information between themselves such that the two autotrophic strains "filled in" the genetic gaps and created a phototropic strain.

William Hayes

Discovered that one cell transfers some or all of its genome to another (donor and recipient relationship), and discovered the fertility factor (F), later determined to be plasmid borne.

Cavalli-Sforza

Found an unusual F+ strain at a 1000 fold higher rate than normal F+ -- Hfr: high frequency of recombination; In crosses with F- strains, virtually no F- parents were converted to F+ of Hfr; Normally, F+ strains convert large fraction of F- parents into F+.

Exogenote

DNA that is transferred to recipient

Endogenote

genome of recipient

F+

F factor normally exists as an independent plasmid.

Hfr

F factor present, integrated into bacterial chromosome, high frequency donor.

Interrupted-mating conjugation

Makes gene mapping possible on bacterial chromosomes (via time in mins); also demonstrates that genes enter sequentially.

Single crossover

Does not result in a viable bacteria recombinant. For a linear fragment to replace a region of recipient chromosome while preserving chromosome continuity, 2 crossover events needed.

Excise

To cut out of; remove

Competent bacteria

Possess the ability to pick up free DNA (from dead bacterium) from the environment [active process].

Homologous recombination

In competent bacteria, if the incoming DNA contains sequences homologous to a region of the chromosome, it can align with that region and undergo homologous recombination.

Bacteriophage

A virus that infects bacteria (can have DNA or RNA genomes)

Petri dish plaque

Clear areas of petri dish agar.

h genes

Influence whether a phage can infect two different E. Coli strains.

r gene

Determines whether the phage quickly or slowly triggers lysis.

Phage cross

Made by doubly infecting the host cell with two parental phages possessing opposing genes --> opportunity for homologous recombination.

Virulent phage

Phage that immediately lyse and kills host cell (only have lytic cycle)

Temperate phage

Can remain within host for a period of time without killing it. (lytic and lysogenic cycle)

Prophage

A phage genome that has been inserted into a specific site on the bacterial chromosome.

Lysogen

a bacterium containing a prophage

Phage transduction

Genetic material can be transferred between bacterial cells via phages carrying donor genes and infecting another bacterium via transduction

Generalized transduction

Transducing phage can carry any part of the bacterial chromosome.

Specialized transduction

Transducing phage is limited to only carrying specific parts of the bacterial chromosome (ex, lambda)

Generalized transduction application

Generalized phages can allow for linkage inferrences from cotransduction; the closer two genes are, the more frequently they will be cotransduced.

Lambda phage

A specialized transducing phage that inserts by a crossover at a specific site in the genome (attP is preferred binding site on phage genome) of the phage and the genome of the bacteria (attB region of bacteria genome).

Lambda prophage immunity

Presence of lambda prophage provides immunity to the same or closely related phages.

Typical lambda outlooping

Results in a complete phage plasmid with no extra DNA from bacteria.

Rare abnormal lambda outlooping

Results in an incomplete phage plasmid that contains some bacterial DNA. Can still cause genetic changes in host DNA.

Transposable element

Segment of DNA that can move spontaneously within or between chromosomes.

Transposon

A sequence that can be translocated even in the absence of complementary sequence in host DNA; cause mutations in nature and increase genetic diversity; used as tools to knock genes out, generate DNA sequencing libraries, or do other tasks.