genetics chapter 9

prototrophic bacteria

wild type (can grow on minimum medium)

auxotrophic bacteria

nutritional mutant (needs complete medium)

minimum medium

includes carbon source, salts, requires bacteria to synthesize most compounds (amino acids, vitamins, etc.) itself

complete medium

contains all substances required by all bacteria

defined medium

lacks just one or a few amino acids or vitamins

bacteria colony

pile of bacteria cells in one spot on petri dish, all derived from one cell following many rounds of cell division - genetically identical

replica plating

test ability of bacteria to synthesize various essential compounds - use defined medium

3 types of gene transfer in bacteria and definitions of each

conjugation - direct transfer of dna from one bacterium to another

transformation - bacterium takes up free dna

transduction - bacterial viruses take dna from one bacterium to another

bacterial genome

usually 1 large circular double stranded dna molecule per cell

plasmids

small circular dna molecules - independent of chromosome

episomes

plasmids that can replicate autonomously, but can also integrate into bacteria chromosome

f factor

episome that includes genes that allow cell to make a s3x pilus

Hfr cells

(high frequency recombination) - f factor integrated into chromosome

integration of f factor into bacterial chromosome via crossing over (F+ to Hfr) happens at a high or low frequency

low

cell types present after F+ and F- conjugation

two F+ cells

cell types present after Hfr and F- cell conjugation

one Hfr cell one F- cell

in conjugation between Hfr and F- cells, what is the end result/behavior of chromosomes

crossing over takes place between Hfr chromosome and F- chromosome

F- chromosome has recombinant alleles

linear chromosome in F- cell from Hfr cell is degraded

using interrupted conjugation to map locations of bacterial genes

allow cells to mate, then interrupt conjugation at a series of time points

genes closest to integrated F factor transferred first

the farther genes are from F factor, the longer it takes for them to be transferred to F- cell

By using different Hfr strains that have F factor at different chromosomal sites and/or in different orientations, can generate more complete maps

F’cell

F factor may be excised from Hfr chromosome and bring some chromosomal dna with it

where does crossing over take place to form F’ cell

within Hfr chromosome

cell types present after conjugation between F’ and F- cell

two F’ cells (partial diploids)

competent cells

cells able to take up dna through their cell membranes

what happens to one strand of dna as it enters a competent cell for transformation

it is destroyed

resulting cells after transformation

one nontransformed, one transformed

cotransformation

transfer of 2 or more genes together to recipient cell

genes that are closer to each other in donor dna are more likely to be on the same dna that integrates into recipient cell’s chromosome

bacteriophage

virus that infects bacteria cells

prophage

integrated phage dna

virulent phage

only able to reproduce by lytic cycle

temperate phage

able to enter lytic or lysogenic cycles

plaques

cleared spots on bacterial lawn due to multiple lytic cycles

how are bacterial genes able to transfer without coming into contact with each other

transduction: phage take dna from one bacterium to another

generalized transduction

random fragments of bacterial chromosomal dna included inside new phage particles instead of phage dna

transducing phage

releases dna into recipient cell and dna integrates into chromosome by crossing over

transductant

received dna from phage

interrupted conjugation works well for mapping relative positions of genes that are far apart, but has low _____

resolution

DNA Viruses

adenoviruses

herpesviruses

papillomaviruses

parvomaviruses

rna viruses

retroviruses

negative strand rna viruses

positive strand rna viruses

follwing retrovirus entry into the cell, reverse transcriptase…

synthesizes dsDNA copy of virus’ RNA genome

retrovirus DNA copy is integrated into the…

host cell chromosome, creating a provirus

two things that could happen to provirus

• remain silent and replicate like other genes

• or can be transcribed to make viral proteins and viral genomic RNA and new virus particles

formation of hiv

SIVcpz evolved from recombination between two different retroviruses that infect monkeys. Humans likely infected by virus that evolved to become HIV-1 through contact with chimpanzees. (example of zoonotic virus)

influenza A subtypes classified on basis of which 2 surface proteins

hemagglutinin (HA) and neuraminidase (NA)

influenza evolution - antigenic drift

error prone replication of RNA genome results in high mutation rate

influenza evolution - antigenic shift

reassortment of RNA strands from different influenza strains.

genome: 8 separate RNA fragments

when an animal is simultaneously infected by 2 different influenza strains, new viruses may contain new combination of RNA fragments

rhinoviruses

responsible for most common colds

small (7200 nucleotides) positive strand genome