Review Questions yeast lecture 23.03.2015
1. 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.), cheap and easy maintenance are important
features
2. 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.
3. 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
4. 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)
5. What segregation ratio would you expect of a mutant versus a wild-type phenotype if the
phnotype 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)
6. 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
7. 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: (7+8.5): 100 x 100 = 15.5% recombination
8. 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.
9. 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
10. Which mutations in the adenine biosynthesis pathway cause the production of a red
intermediate (1)
ade2, ade1
11. What color will colonies of an ade2, ade8 double mutation display (look at the pathway!)
(1)
White ; ade8 acts upstream of ade2