Lecture 10 - Model Organisms and Eukaryotic Molecular Genetics: Simon Whitehall Flashcards
What is a Model Organism?
A well established experimental biological system.
What are the 5 key features of a model organism?
- Rapid maturity
- Easily manipulated
- Short life span
- Large no. of offspring
- Readily available.
Why do we need Model Organisms?
K type species (such as humans) are unsuitable for studying developmental genetics. R Type species have…
rapid maturity easily manipulated short life span readily available many offspring small in size
What are the 3 categories of model organisms?
Genetic: Species suitable for genetic analysis, lots of offspring, short generation time and allows for detailed genetic maps and has a sequenced genome.
Genomic: Occupy a special position in the evolutionary tree.
Experimental: May not be easy to manipulate but have certain other advantages.
What is the model organism for bacteria - and what are it’s advantages?
Escherichia Coli
Gram negative rod shaped bacteria.
Rapid generation.
Safe lab strains available.
Very easy to manipulate and transform
Sequenced genome.
What is the alternative model organism for bacteria
Yeast ( S.Cerevisiae & S.Pombe )
What is the model organism for plants?
A.thaliana
What is the model organism for Insects?
Fly : Drosophilia
What is the model organism for the worm?
C.elegans
What is the model organism for fish?
Zebrafish
What is the model organism for mammals?
Mouse
What is a homologue?
A gene related to another gene by descent from a common ancestral DNA sequence.
What is an orthologue?
A gene related to another gene from different species. Usually retain the same function over course of evolution.
What is a paralogue?
Genes related by duplication within a genome.
What is the difference between a homologue and an orthologue in a model organism?
A homologue is a general term for a gene related to another gene by descent from a common ancestral DNA sequence. It does not specify whether this is between members of the same species, or different.
The definition of an orthologue provides this clarity, this is specifically between different species.
What is gene knockout?
Where a gene sequence(s) are completely or partially removed and gene expression is completely eliminated.
What is gene knockdown?
Techniques that reduce/interfere with the expression of the gene. It interferes with mRNA, and can introduce a double stranded mRNA (which is complimentary to mRNA) - thereby destroying mRNA!
What are the properties of S.cerevisiae? (aka Bakers yeast)
Budding division
Linear Chromsomes
Unicellular Eukaryote
Shares basic biological properties with humans
20% of human disease genes have orthologues in yeast.
Is evolutionarily divergent with Fission yeast.
What are the properties of S.pombe? (aka Fission yeast)
Fission division (splits to divide) Nuclear genome with 3 linear chromsomes.
Is evolutionarily divergent with Bakers yeast, contains genes that are missing in bakers yeast but present in humans.
What are the properties of Arabidopsis thaliana?
Has a small genome (for a plant) with few gene duplications and repetitive sequences.
Easy to generate mutants using mutagens.
Self pollinates - so can create homozygous recessive mutations.
Cross polination -> Genetic mapping or strains with multiple mutations.
Can be transformed with Foreign DNA using the Ti plasmid from Agrobacteriam tumefaciens.
Useful to study flowering sensitivity light and plant development.
What are the properties of Drosophilia?
3 pairs of autosomal chrosomes, plus X & Y chromosomes.
Easy to cross, with huge number of mutants available.
Many phenotypic markers.
Mature larvae produce GIANT POLYTENE CHROMSOMES allowing genetic mapping.
Transformable using P Element ransposon and other transposons - which can then create deletion and insertion mutations.
What is a disease model?
A mutant model organism that mimics the phenotypes/features observed in a human disease
What mutations do drosophilia have that act as a Disease model for SMA?
Carry a SMN gene which is orthologous to humans.
What are the properties of C.elegans?
Transparent - easy observation.
2 sexes hermaphrodites and males allowing for genetic crossing.
40% of genes have human orthologues.
Easy to perform genetic crsoses
Many mutants available
Transformable
Genes can be knocked down using RNA interference.
What are the properties of Zebrafish?
Transparent embryos - can see changes.
- Difficult to sequence
Possible to make mutants by random mutagenesis
Knockdown of expression fo specific genes is possible using morpholinos.
What are the properties of Mice.
Closely related to humans.
78.5% genes orthologous to humans.
Manipulation of embryonic stem cells -> Transgenic mice which contain additonal foreign DNA which can be used to study and make links with human diseases.
Mouse knockouts possible.
What is pronuclear microinjection?
Foreign DNA introduced directly into (mouse) egg just after fertilization.
What is the introduction of DNA into embryonic stem cells?
ES cells form the very early mouse emrbyo differentiate into all types of cell when introduced into another embryo.
Name a mouse disease model.
ob/ob mouse, eats excessively -> obese, mutations in gene responsible for hormone LEPTIN which is involved in controlling appetite.
What is a transgenic animal?
A transgenic animal is one whose genome has been changed to carry genes from other species.
