Lecture 35 Flashcards
what are model organisms
non human species used to study a specific biological phenomenon or disease
why do we use model organisms
cant experiment on human so we need to learn from other organisms
what are the characteristics of model organisms
mimic specific aspects of human biology
are somewhat easy to work with
what are model organisms often used for
forward or reverse genetics
what are reverse genetics
genotype –> phenotype
knockout mouse, role of gene on phenotype
what are forward genetics
phenotypes to genotype
what genes regulate trait
name and describe eukaryotic model organisms
s cerevisiae (easiest to grow, least like humans)
c elegans
d melanogaster
danio rerio
mus musculus (hardest to grow, most like humans= diverges from humans more recently in tree)
Describe s cerevisiae
eukaryotic
unicellular fungus
generation time = 2-3 hrs (amount of time offspring becomes able to reproduce)
can exist as haploid or diploid
can reproduce sexually or asexually
can be frozen and revived
describe life cycle of S. cerevisiae
haploid - asexual reproduction
haploid in stress conditions = easier to know effect of gene = easy to mutate since one copy
mates toeter and reproduces = diploid
helps undersatnd relationship between diff genes and diff copies of same genes and diff genes
describe c elegans
invertebrate eukaryote
mutlicellular
generation time = 3 days, 300 progeny = many
extremely simple, translucent - helps understand development
can trace fate of each cell = 1090 total = invariant development tree = every adult made of same # of cells and develop in same exact way
two sexes = male and hermaphrodite - can be self fertilized and be crossed
can be frozen and revived
describe life cycle of c elegans
embryo - 12 hrs later, not too long embryonic development, leads to full worm
if in conditions of crowding, starvation or high temp = leads to dauer = like quiescence then several months later leads to full worm
describe d melanogaster
more similar to humans - similar cns, body plan, musculoskeletal aspects and digestive tract
invertebrate animal
mutilcellular
generation time = 10 days, 100 progeny
more complex than c elegans
share 75% of human disease causing genes
very well studied, many genetic tools
describe danio rerio
vertebrate animal
multicellular
generation time = 2-3 months, 200 eggs
optically translucent embryos and larvae
relatively simple and inexpensive to maintain
easily treated with small molecules for drug and toxicity screens - easier since grown in water
closer to humans for biological purpsoes = melanocytes
describe mus musculus
vertebrate mammal
generation time = 3 months, 2-12 pups
small easy to house for mammals
commonly used to study human biology, preform preclinical testing
mice are not always perfect models for humans, many differences stills
describe 2 emerging model organisms to study unique phenomena
do things humans cant
axolotl = can regrow limbs
planaria = can regenerate everything, whole body of stem cells
describe basics of forward genetic screens - 3
pheno –> geno
1 - pertrubs lots of genes - randomly or systemically
2 - look for specific phenotype - organism dies, changes in some specific way
3- figure out which gene mutated
describe Finding cell division cycle (cdc) mutants in S. cerevisiae - gen
cell cycle easy to see in yeast
g1 s g2 m - look at stuck cells - phenotype
describe temp sensitive mutations to study cell cycle
at permissive temps = grows normally
are restrictive temps = doesnt fold properly and leads to mutant
describe replica plating
to isolate temp sensitive mutants
add mutagen to yeast, master plate, use sticky sterile velveteen, imprint colonies and test at diff temps
at high temp = mutants dont grow
WHAT DID they find from cdc mutants - 3 diff mutants
cdc1 mutant = never keeps going, frozen in g1
cdc2 mutant =form bud but freeze not far in, frozen in s
cdc3 mutant = cytokineses cannot happen, late stage mitosis affected
what do cdc mutants correspond to
cell cycle genes and other stuff
cdc1 = make cell wall
cdc2 = dna pol
cdc3 = septin - important for cytokinesis
what can yeast be used to preform and explain
Complementation
used to test if 2 mutant strains have mutations in same gene
should be fine if one has wild type of each gene - if not on same gene
how to identify mutant genes - 4 main aspects
make genetic library and does rescue experiments
1 - introduce diff plasmids into yeast, test which plasmids rescue mutant
2 - Sequence plasmids that rescue to identify yeast gene responsible for phenotype
3 - introduce diff cdnas into yeast and test which rescue mutant
4 - sequence cdnas that rescue to identify human gene responsible for a phenotype
describe identifying the human version of cdc28
use mutant and human cdna library, extract and sequence plasmids = colonies survived are rescued
cdc 2 (s pombe) = cdc28 (s cerevisiae) = cdk1 (human) - very conserved
