Download 1.We wish to locate these four genes on the chromosomes. We don`t

Concepts in Modern Genetics, Part Y. Barral
Questions:
1.We wish to locate these four genes on the chromosomes. We don’t know whether they
are all on one chromosome or on different ones. The only information available is the
table with crossing results:
Ab x aB: 47 PD, 51 NPD
Bc x bC: 40 PD, 38 NPD, 168 TT
Ad x aD: 40 PD, 40 NPD, 60 TT
Cd x cD: 40 PD, 3 NPD, 80 TT
a) Calculate the distances between each gene, and show which genes are linked/ on the
same chromosome etc.
b) Comment on why you were able to obtain the information you did? Is there any
information missing ?
c) What would be the ratios of PD, NPD, TT if all the genes were close to the centromere
and on different chromosomes?
d) What would be the ratios of PD, NPD, TT if all the genes were not close to the
centromere and on different chromosomes?
2.You know that E, F and G genes are linked. Here are the results of the crossings. Draw
the genes on a chromosome and calculate the distances between them. Hint: This is not
a tetrade analysis. Do not forget that closer the two genes are located, the less is the
chance of a crossover taking place between them.
Genotype
EFg 389
efG 413
EFG 60
efg 68
eFg 29
EfG 34
Efg 3
eFG 4
Concepts in Modern Genetics, Part Y. Barral
3.
a) Would the following strains grow on yeast minimal media without leucine (i.e. Leu+)?
(circle
yes or no)
# Markers (all are genetically unlinked) Growth on SD-leu
1) MATa, ade2, ura3-52, leu2-3, his3, trp1-1, Yes No
2) MATα, ura3-x, leu2-11, his3, trp1-1 Yes No
3) MATa, MAL2, ura2, Δleu3, his3, trp1-1 Yes No
4) A diploid strain resulting from Strain #1 mated with Strain #2 Yes No
5) A diploid strain resulting from Strain #2 mated with Strain #3 Yes No
b) If diploid strain in #4 is sporulated what percentage of the spores on average would
you
expect to be Leu+?
c) If diploid strain in #5 is sporulated what percentage of the spores on average would
you expect
to be Leu+?
4.Diploid and haploid yeast cells behave differently with respect to their ability to mate,
respond to pheromones or undergo meiosis. With the help of drawings, explain what is
the genetic basis for these differences.
5. A screen for mating type switching deficient mutants has been carried out. One
of the mutations, called swi-A3, has the following features:
The swi-A3 trp1 MATa strain is crossed with a wild type (SWI+ TRP1+ MATalpha), the
diploid is sporulated and the spores are dissected. In each tetrad, two spores are
deficient for mating type switch, and two spores are proficient. The tetrads obtained were
as follows:
42
112
1
45
trp1 swi- MATa
trp1 swi- MATa
trp1 swi- MATa
trp1 SWI+ MATα
trp1 swi- MATa
TRP1 swi- MATa
trp1 SWI+ MATa
trp1 SWI+ MATα
TRP1 SWI+ MATα
trp1 SWI+ MATα
ΤRP1 swi- MATα
TRP1 swi- MATa
TRP1 SWI+ MATα
TRP1 SWI+ MATα
TRP1 SWI+ MATα
TRP1 swi- MATa
So what can we learn from this ?
6. Suppose a number of adenine-requiring mutants were isolated from a newly isolated
fungi and the mutations have been classified into complementation groups. Each gene is
thought to code for an enzyme in the biosynthetic pathway for adenine, so each mutation
causes a block at a different step. All the mutations are recessive.
Some of the ade- mutants form pink colonies when grown on supplemented agar plates.
Presumably, in some of the mutants a metabolic intermediate accumulates to high levels
and causes the pink color. Use the results shown below to determine the order of action
for the products of these genes.
Concepts in Modern Genetics, Part Y. Barral
Mutant
Colony Color
ade2
pink
ade6
pink
ade10
white
ade12
white
ade2,ade10
white
ade2,ade6
pink
ade2,ade12
pink
ade6,ade10
white
ade6,ade12
pink
ade10,ade12
white