Model Organisms
Honors Genetics
Chapter 2
Organism 1
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.html
Mammalian
http://www.ncbi.nlm.nih.gov/About/model/otherorg.html
Other
Yeast –Saccharomyces cerevisiae
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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
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]
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
Yeast Cells - TEM
Yeast Cells – Phase Contrast
Yeast Cell Types
 Mating types(a and alpha)
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Attraction via pheromones
Mating
Shmoo formation
Budding
Asexual cell formation
Sporulation
Short life cycle
Easily manipulated in laboratory
Easily cultured
Non-pathogenic
Yeast Cell Types
Mating
Yeast Genome
http://www.yeastgenome.org/
http://biol.org/Yeasts.htm
Gene Maps
http://db.yeastgenome.org/cgi-bin/PGMAP/pgMap
Gene Example
 http://www.bio.davidson.edu/courses/ge
nomics/2001/madden/assignment2.html
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
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.
Supplies
 Get all supplies from lab table
 Return all supplies to lab table
 Clean up lab bench