Announcements Ms. Laina Long from the UCLA Bridges Program will give a brief presentation today at 10:40 in this room. She will give you an overview of this paid summer research internship program at UCLA and can answer any questions you may have. Essay exam on Friday. I do want to state that while the genetics portion is focused a problem solving format there could be a definition, result to interpret or genetic concept to briefly explain. The emphasis is on the genetic problems. The next problem will be due on THURSDAY March 13 th instead of Tuesday March 11 th.

Ch. 8 Viral Genetic Systems part 2

Various viral shapes Influenzya A Ebola Herpes HIV

Viruses: highly varied RNA containing or DNA containing Single stranded or Double stranded Linear or circular

Bacteriophages & Transduction Transduction: gene transfer from virus to bacterium –Virulent phages lytic –Temperate phages lysogenic

Virulent Bacteriophages & Lysis

Viral Plaques “clear spaces” This “cloudy:area is living bacteria

But: Temperate Phages are Lysogenic Bacteriophages

Transduction: Using Phages to map bacterial genes E. coli

Generalize Transduction Requires lytic bacteriophages Bacterial chromosome degraded Phage can transfer & recombination bacterial gene to different bacterium Rare event

Evidence to support transduction

Mechanism for: Generalized Transduction

Mechanism of Generalized Transduction (one more time)

Evidence to support & calculate frequency of recombination following transduction

h - r + X h + r - PhenotypeGenotype Clear and smallh - r + Cloudy and largeh + r - Cloudy and smallh+r+h+r+ Clear and largeh-r-h-r- Progeny Phage produced EXPERIMENT SUPPORTING PHAGE RECOMBINATION

Count colonies by phenotypes: corresponds to genotypes Determine parental phenotye Determine recombinant phenotype

Specialized Transduction “Targeted transfer of genes: genes must be located at specific site on bacterial genome! Location, location, location!

Specialized Transduction Gene transfer from phage to bacterium Site specific transfer Requires lysogenic bacteriophages Lambda phage one of the best studied

a. Movement of the prophage

b. Another possible movement of prophage

Now what could happen. Leads to unstable transductant Leads to stable transductant

Unstable Transductant

Fine Structure Analysis of Bacteriophage genes Early studies on the structure of a “gene” go beyond recombination experiments Mutations were studied in phage Are mutations within the same gene or affecting different genes? Transduction is used to answer these questions. Let’s now look how these studies taught us some key facts about genes.

Okay, this sounds familiar

Yes, recombination could be observed with these mutants.

Let’s take this one step further Complementation experiments using transduction The question is: where do these mutations exist? –Within the same gene or on different genes?

Genes may overlap in the viral and prokaryotic genomes!