Model organism and experimental approaches

What makes good model organism

Size, generation time, embryo accessibility, organism type and phylogenetic position, ease of experiment manipulation

Arabidopsis thaliana

Thale cress plant, grow and produce thousand progeny after 8-10 weeks, both gamest in same plant 9makes ova and sperm), can undergo genetic transformation, small genome fully sequenced

Drosophila melanogaster

fruit fly, small size, short life cycle (10 days), high fecundity (~500 eggs) fully sequence genome, conservation of developmental process (conserved to other species)

Caenorhabditis elegans

roundworm, easily grown in petri dishes, transparent body, zygote to mature in 3½ days, simple anatomy (959 somatic cells), fully sequence genome, complete cell linage mapped

Xenopus laevis

African clawed frog, large embryo size that can be cultured, rapid development - good for transplantation experiment, external fertilization and development

Gallus gallus

Jungle fowl, large obtainable eggs, easy to manipulate, complex development similar to mammal

Mus musculus

Mouse, genetic similarities to human (90%), manupulable genome (ex: knock out), easy to breed and maintain, fully sequence genome

Homo Sapiens (stem cells)

Ethical consideration about human embryo experiments, Biopsy and post mortem samples, stem cells and in vitro models

Direct Observation in Dev bio

use microscope to trace descendant of particular cells,

Fate map

diagram, shows what will become of each region of the embryo during normal development

Vital dyes

marking specific cells of embryonic surface with, Walter Vogt’s method, fades as cell divides (dilutes)

Fate mapping with fluorescent

specific cell injected with fluorescent dye, doesn’t fade like vital dyes

Chimeric embryos

genetic labelling, can fate map with transgenic dna

Immunohistochemistry/Immunofluorescence process

Protein in fixed cell/Antigen recognized by primary antibody, secondary antibody conjugated enzyme/Fluorophore indicated presence

In Situ Hybridization (ISH)

allow precise localization of specific segment of nuclei acid, antisense DIG-labelled RNA probe hybridizes to expressed odd skipped gene, alkaline phosphatase conjugated antibodies bind hybridized probe, convert NBT (nitro blue tetrazolium chloride) and BCIP (5-Bromo-4-chloro-3-indolyl-phosphate) into blue precipitate

CRISPR/Cas9 mediated gene editing

gRNA directs Cas9 to where dsDNA break wanted, Non-homologous end joining (knock out) or Homology directed repair (Insertion)

CRE-lox technique

bacteria enzyme Cre recombinase recognize specific DNA sequence (loxP), deleted DNA between 2 LoxP sites, knock out technique

yellow cytoplasm in tunicate cell

contains macho mRNA that governed muscle development

Steps of FIND it, Lose it, Move it

Find - association between, Lose - is it necessary, Move - sufficient for the process