Model Organisms Honors Genetics Chapter 2 Organism 1

What is a model organism? Non- 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. Mammalian Other

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

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) bp

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)  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 /

Gene Maps

Gene Example  nomics/2001/madden/assignment2.html nomics/2001/madden/assignment2.html 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.  When plates have grown out. Place in refrigerator.

Supplies  Get all supplies from lab table  Return all supplies to lab table  Clean up lab bench