Download Review Questions yeast lecture 18

Review Questions yeast lecture 20.01.2017
1. Have a look at the text (Yeast) Genetics vs. Biochemistry – The Salvation of Doug/The
Demise of Bill, which you can find in Noppa. In your understanding of the text, what in
your opinion are the major differences between biochemical and yeast genetics
approaches? (2)
Geneticists generate a variation (typically a loss – of function mutation)
and observe the consequences on their model system they investigate
and interpret these observations in the context of the problem they are
working on. Biochemists separate components of their system by
physical and chemical means and analyze the individual components
and their properties - interpret these observations in the context of the
problem they are working on…
2. What is a model organism (=what are the basic requirements for a model organism) (1)
A model for certain aspects of human cellular, developmental or genetic
processes. Require similarity to humans in at least some aspects. Short
reproduction time, large number of offspring, ease of manipulation
(generating mutants etc.) and cheap and easy maintenance are
important features.
3. What is the basic difference between complex media like YPD and synthetic media (1)
The content of synthetic media is known, while the exact composition of
complex media is not.
4. Define homothallic versus heterothallic growth (2)
Homothallic growth implies that yeast cells are able to mate with their
offspring due to the ability to switch mating type. These strains
immediately convert form haplo to diplophase after spore growth.
Heterothallic yeast strains are unable to switch mating type and cannot
mate with their offspring. Therefore, they can be maintained in haploid
form
5. Why does the existence of a haploid growth phase in S. cerevisiae give it an advantage
over most other eukaryotic organisms (in terms of usefulness to the researcher)? (1)
Phenotype of mutation apparent immediately. Every haploid strain is a
“pure bred” strain for its genetic traits. (Also: Sporulation = Meiosis;
products of the same meiotic event can be examined)
6. What segregation ratio would you expect of a mutant versus a wild-type phenotype if the
phenotype was cause by a mutation in one gene? What about if simultaneous mutations in
TWO unlinked genes were required to get the phenotype (why? Be ready to draw out!)
(3)
2:2 if in one gene (see lecture). 3:1 if in two (unlinked) genes
(will be explained)
7. In the analysis of linked genes, what does the amount of TT tetrads obtained depend on?
Why? (1)
Depends on the distance of the two linked genes. The further the
distance, the higher the probability for recombination
8. You have two mutant haploid strains, one with a mutation in the Leucine biosynthesis
pathway, the other with a mutation in the Uracil biosynthesis pathway. The diploid
resulting from mating is Ura+, Leu+. After dissection of 100 tetrads, 76 of them are PD,
7 of them are NPD and 17 are TT. What are the PD, NPD and TT phenotypes? Are these
genes linked? If so, determine the genetic distance of these genes. (3)
Genes are linked PD >>1, NPD <<1.
Distance: (14+15): 200 x 100 = 15.5% recombination
9. Why is complementation analysis necessary during the analysis of mutations? Be ready
to sort mutations into complementation groups (I will provide the table with the results of
complementation analysis) (3)
Complementation analysis reveals if mutations are in the same or in
different genes.
10. How can epistasis analysis be helpful in the characterization of a pathway? (1)
Epistasis analysis can reveal the position of two different mutations in a
pathway relative to each other
11. Which mutations in the adenine biosynthesis pathway cause the production of a red
intermediate (1)
ade2, ade1
12. What color will colonies of an ade2, ade8 double mutation display (look at the pathway!)
(1)
White ; ade8 acts upstream of ade2