Model Model OrganismsOrganismsHonors GeneticsHonors Genetics

Chapter 2Chapter 2

Organism 1Organism 1

What is a model organism?What is a model organism?

http://www.ncbi.nlm.nih.gov/About/model/nonmammal.htmlNon- Mammalian

Over the last century, research on a small number of organisms has played a pivotal role in advancing our understanding of numerous biological processes. This is because many aspects of biology are similar in most or all organisms, but it is frequently much easier to study a particular aspect in one organism than in others. These much-studied organisms are commonly referred to as model organisms, because each has one or more characteristics that make it suitable for laboratory study.

http://www.ncbi.nlm.nih.gov/About/model/mammal.htmlMammalian

http://www.ncbi.nlm.nih.gov/About/model/otherorg.htmlOther

Yeast –Yeast –Saccharomyces cerevisiaeSaccharomyces cerevisiae

Unicellular fungusUnicellular fungus EukaryoteEukaryote Complex life cycleComplex life cycle Exists in the diploid and haploid stagesExists in the diploid and haploid stages Has mating types in the haploid stateHas mating types in the haploid state Mates to form a diploid organismMates to form a diploid organism 32 chromosomes32 chromosomes Many biochemical variantsMany biochemical variants Genome completedGenome completed Economically important organismEconomically important organism

Yeast ChromosomesYeast Chromosomes

Entire genome sequenced (12 Mb; Entire genome sequenced (12 Mb; 6,200 genes) 6,200 genes)

Centromeres small (~120 bp), unique; Centromeres small (~120 bp), unique; three regions bind proteins, allowing three regions bind proteins, allowing interaction with a single microtubule interaction with a single microtubule for segregation; no transcriptional for segregation; no transcriptional silencing at centromeres silencing at centromeres

Telomeres (TG1-3)n [Note that human Telomeres (TG1-3)n [Note that human telomere sequence is (TTAGGG)n] telomere sequence is (TTAGGG)n]

Replication origins (ARS elements) 100-Replication origins (ARS elements) 100-150 bp150 bp

Yeast GenesYeast Genes

Yeast genes are given three Yeast genes are given three letter abbreviationsletter abbreviations

Genes are named after the Genes are named after the protein that they encodeprotein that they encode

Wild type genes( dominant) Wild type genes( dominant) begin in upper case lettersbegin in upper case letters

Mutants or recessive begin Mutants or recessive begin in lower casein lower case

Yeast Cells - TEMYeast Cells - TEM

Yeast Cells – Phase ContrastYeast Cells – Phase Contrast

Yeast Cell TypesYeast Cell Types

Mating types(Mating types(aa and and alphaalpha)) Attraction via pheromonesAttraction via pheromones MatingMating Shmoo formationShmoo formation BuddingBudding Asexual cell formationAsexual cell formation SporulationSporulation Short life cycleShort life cycle Easily manipulated in laboratoryEasily manipulated in laboratory Easily culturedEasily cultured Non-pathogenicNon-pathogenic

Yeast Cell TypesYeast Cell Types

MatingMating

Yeast GenomeYeast Genome

http://www.yeastgenome.org/

http://biol.org/Yeasts.htm

Gene MapsGene Maps

http://db.yeastgenome.org/cgi-bin/PGMAP/pgMap

Gene ExampleGene Example

http://www.bio.davidson.edu/http://www.bio.davidson.edu/courses/genomics/2001/madden/courses/genomics/2001/madden/assignment2.htmlassignment2.html

Culture of YeastCulture of Yeast

• Complex media

• YED- Yeast extract dextrose – Yeast extract and glucose

• YEAD – Yeast extract dextrose with an excess of adenine

• MV- Minimal media ( no adenine ) – This medium should support wild type

Aseptic TechniqueAseptic Technique

Use disinfectant on work areaUse disinfectant on work area Use fresh sterile media. Yeast media is placed in Use fresh sterile media. Yeast media is placed in

Petri Dishes . Remove from refrigerator. Warm to Petri Dishes . Remove from refrigerator. Warm to room temperatureroom temperature

Use sterile toothpicks for transfer of yeastUse sterile toothpicks for transfer of yeast Work with care to limit exposure of plate to the airWork with care to limit exposure of plate to the air Dispose of all toothpicks in cup on desk. Empty cup Dispose of all toothpicks in cup on desk. Empty cup

into hazardous waste bag.into hazardous waste bag. Label all plates with date, your initials, experiment, Label all plates with date, your initials, experiment,

and other pertinent facts.and other pertinent facts. Incubate cultures agar side up at room temperature. Incubate cultures agar side up at room temperature.

Secure with tape on edges to insure Petri Dish does Secure with tape on edges to insure Petri Dish does not open.not open.

When plates have grown out. Place in refrigerator.When plates have grown out. Place in refrigerator.

SuppliesSupplies

Get all supplies from lab Get all supplies from lab tabletable

Return all supplies to lab Return all supplies to lab tabletable

Clean up lab benchClean up lab bench