GENETIC SCREENS AND MATERNAL EFFECTS Flashcards
Pros and cons of using Drosophila as a model for developmental analysis…
PROS : - small
- short generation time
- early development easily visualised
- each female produces several hundred eggs
- long history of research has provided scientists with drosophila info on a community wide basis
- only 4 chromosomes
CONS: - cannot self fertilise
- can’t freeze, have to be living stocks
1) What is the key issue when studying development in flies?
2) What is the long winded solution?
1) the mutations in development toolkit genes are often recessive lethal and the flies die too early
2) laborious breeding technique
What are balancer chromosomes/ what are their use and how do they work?
WHAT - chromosomes with multiple inverted repeats
WHY - in order to maintain heterozygote stock in a living population
HOW - the multiple inverted repeats prevent recombination but also maintain a mutation
- carry the mutation
- also carry a dominant marker, such as curly wings in order to provide evidence that the balancer chromosome is there
What will occur if an organism has two copies of a balancer chromosome?
- they will die as they have two copies of the recessive lethal mutation
Then how are balancer chromosomes used once they are obtained?
Two heterozygotes will be crossed
- those with development mutation can be observed
- will maintain a viable population of heterozygotes (seen by curly wings)
Mutations in toolkit genes are very (a). Therefore how are mutations created (b)?
For a gene of average length, about (c) gametes will carry a mutation in that gene
a) rare
b) using mutagens such as ethyl methane sulfate (EMS)
c) 1/1000
Why are mutations often introduced to the F0 male generation?
What is the product?
- males produce millions of sperm
- each F1 fly produced has a unique and are heterozygous for novel mutations
Sib matings are done in which generation(s)? Why?
F2 to produce F3
- to uncover homozygotes in F3
Why are maternal effect mutations not seen phenotypically until F4?
- early acting genes are expressed in the mother and deposited as mRNA or protein in the embryo
- therefore, the F3 generation which will have heterozygote parents will be given functional maternal genes deposited in egg
- when this female becomes an adult, it is homozygous- and cannot produce functional proteins for its child
Map based cloning used (a) markers but is too (b) and tedious.
a) linked
b) slow
What is transposon tagging?
- disrupt genes and isolate DNA from affected gene
Snapdragon flowers are usually (a) but mutants are (b). The (c) gene encodes for the enzyme needed for (d) pigment.
a) red
b) white
c) Pallida
d) anthocyanin
Describe the phenotype of a pal-2 mutant?
- mostly white with patches of red
Why does the pal-2 mutant have a much larger gene than other mutants?
- Contained transposable elements called Tam3
What does Tam3 do?
- contains nucleases which aid in transposition, allowing it to insert into the Pallida gene and disrupt it- meaning 0 production of anthocyanin pigment
- BUT also has to the ability to be excised and restore gene function leading to the production of red cells again
