L3 - Model systems & techniques

Question 1

What are some advantages of using small organisms as experimental model organisms?

Answer 1

• Small genome size
• Short life cycle
• Easy to grow
  -Economical to maintain
• Convenient to observe and study

Question 2

If a gene duplicates and then a speciation event occurs, what are the two types of genes called?

Answer 2

Orthologs & Paralogs

Question 3

What is the difference between them?

Answer 3

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.

Question 4

Characteristics between them both?

Answer 4

Orthologs tend to retain similar functions whereas paralogs tend to acquire a new function.

Question 5

How can we induce a mutation into Drosophila Melanogaster and why would we want to?

Answer 5

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.

Question 6

What point mutations occurs via EMS predominantly?

Answer 6

Cytosine to Thymine

Question 7

Variegating meaning:

Answer 7

To diversify in external appearance especially with different colours

Question 8

What is Position-Effect Variegation (PEV)?

Answer 8

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.

Question 9

Position effect variegation results from chromosome rearrangements which translocate euchromatic genes close to the heterochromatin.

Answer 9

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.

Question 10

What can cause a variegating phenotype?

Answer 10

A change in the position of a gene within the chromosome

Question 11

What is the purpose of Whole Mount in-situ Hybridisation (WMISH)?

Answer 11

To view the location of nucleic acids in situ (in their original place)

Question 12

What is the 1st step for this?

Answer 12

Hole in the membrane. RNA made complementary to specific mRNA. Digoxigenin label on uridine of RNA.

Question 13

2nd

Answer 13

Alkaline phosphatase-conjugated antibody to digoxigenin

Question 14

3rd

Answer 14

Colourless compound that becomes purple dye when phosphate is removed. To highlight where the nucleic acids are. Visualising the expressed RNAs in the embryo.

Question 15

What is meant by a chimeric organism?

Answer 15

Chimeras are organisms composed of at least two genetically distinct cell lineages originating from different zygotes

Question 16

What is the first step in producing a chimeric mouse?

Answer 16

ES cells are derived from a genetically different strain of mice and inserted via a micropippete into a recipient blastocyst.

Question 17

What is the second step?

Answer 17

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.

Question 18

What do organoids derive from?

Answer 18

Stem cells