L3 - Model systems & techniques Flashcards
What are some advantages of using small organisms as experimental model organisms?
- Small genome size
- Short life cycle
- Easy to grow
-Economical to maintain - Convenient to observe and study
If a gene duplicates and then a speciation event occurs, what are the two types of genes called?
Orthologs & Paralogs
What is the difference between them?
Orthologous (or homologous) genes are found in different organisms, but are derived from a single common ancestral gene present in the common ancestor of those organisms. Paralogous genes are genes present in a particular organism that are related to each other through a gene duplication event.
Characteristics between them both?
Orthologs tend to retain similar functions whereas paralogs tend to acquire a new function.
How can we induce a mutation into Drosophila Melanogaster and why would we want to?
EMS (Ethyl Methane Sulfonate) which induces chemical modifications of nucleotides. Systematic genetic screens of the whole genome for mutations affecting the patterning of the early embryo.
What point mutations occurs via EMS predominantly?
Cytosine to Thymine
Variegating meaning:
To diversify in external appearance especially with different colours
What is Position-Effect Variegation (PEV)?
PEV results when a gene normally in euchromatin is juxtaposed with heterochromatin by rearrangement or transposition. When heterochromatin packaging spreads across the heterochromatin/euchromatin border, it causes transcriptional silencing in a stochastic pattern.
Position effect variegation results from chromosome rearrangements which translocate euchromatic genes close to the heterochromatin.
So, ADE2 (gene in the adenine biosynthesis pathway) is inserted near the telomere, variegated phenotype occurs (red and white sectors) rather than just white as the normal phenotype.
What can cause a variegating phenotype?
A change in the position of a gene within the chromosome
What is the purpose of Whole Mount in-situ Hybridisation (WMISH)?
To view the location of nucleic acids in situ (in their original place)
What is the 1st step for this?
Hole in the membrane. RNA made complementary to specific mRNA. Digoxigenin label on uridine of RNA.
2nd
Alkaline phosphatase-conjugated antibody to digoxigenin
3rd
Colourless compound that becomes purple dye when phosphate is removed. To highlight where the nucleic acids are. Visualising the expressed RNAs in the embryo.
What is meant by a chimeric organism?
Chimeras are organisms composed of at least two genetically distinct cell lineages originating from different zygotes
What is the first step in producing a chimeric mouse?
ES cells are derived from a genetically different strain of mice and inserted via a micropippete into a recipient blastocyst.
What is the second step?
Injected cells become incorporated in inner cell mass of host blastocyst. Blastocyst develops in foster mother into a healthy chimeric mouse. The ES cells may contribute to any tissue.
What do organoids derive from?
Stem cells
