Model Organisms

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Model Organisms

• Honors Genetics
• Chapter 2
• Organism 1

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What is a model organism?
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/nonmammal.
html Non- Mammalian
http//www.ncbi.nlm.nih.gov/About/model/mammal.htm
l Mammalian
http//www.ncbi.nlm.nih.gov/About/model/otherorg.h
tml Other
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Yeast Saccharomyces cerevisiae

• Unicellular fungus
• Eukaryote
• Complex life cycle
• Exists in the diploid and haploid stages
• Has mating types in the haploid state
• Mates to form a diploid organism
• 32 chromosomes
• Many biochemical variants
• Genome completed
• Economically important organism

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Yeast Chromosomes

• Entire genome sequenced (12 Mb 6,200 genes)
• Centromeres small (120 bp), unique three
  regions bind proteins, allowing interaction with
  a single microtubule for segregation no
  transcriptional silencing at centromeres
• Telomeres (TG1-3)n Note that human telomere
  sequence is (TTAGGG)n
• Replication origins (ARS elements) 100-150 bp

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Yeast Genes

• Yeast genes are given three letter abbreviations
• Genes are named after the protein that they
  encode
• Wild type genes( dominant) begin in upper case
  letters
• Mutants or recessive begin in lower case

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Yeast Cells - TEM
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Yeast Cells Phase Contrast
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Yeast Cell Types

• Mating types(a and alpha)
• Attraction via pheromones
• Mating
• Shmoo formation
• Budding
• Asexual cell formation
• Sporulation
• Short life cycle
• Easily manipulated in laboratory
• Easily cultured
• Non-pathogenic

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Yeast Cell Types
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Mating
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Yeast Genome
http//www.yeastgenome.org/ http//biol.org/Yeas
ts.htm
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Gene Maps
http//db.yeastgenome.org/cgi-bin/PGMAP/pgMap
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Gene Example

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

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Culture 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

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Aseptic Technique

• Use disinfectant on work area
• Use fresh sterile media. Yeast media is placed
  in Petri Dishes . Remove from refrigerator. Warm
  to room temperature
• Use sterile toothpicks for transfer of yeast
• Work with care to limit exposure of plate to the
  air
• Dispose of all toothpicks in cup on desk. Empty
  cup into hazardous waste bag.
• Label all plates with date, your initials,
  experiment, and other pertinent facts.
• Incubate cultures agar side up at room
  temperature. Secure with tape on edges to insure
  Petri Dish does not open.
• When plates have grown out. Place in
  refrigerator.

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Supplies

• Get all supplies from lab table
• Return all supplies to lab table
• Clean up lab bench