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AdvancedGenetics
YeastMarch,2017
HomeworkProblemSet
1.Forthefollowingtetraddata(PD:NPD:T),stateifthegenesare: A. linkedorunlinked
B. Iflinked,themapdistancebetweenthegenes
C. Centromerelinkage,ifpossible
a. 47:53:0
Unlinked(sincePD=NPD),bothlinkedtocentromere
b. 45:4:51
Linked(sincePD>>NDP)37.5mapunits
c. 20:20:60 Unlinked(sincePD+NPD)notknownifthereiscentromere
linkageorifonsamechromosome
d. 10:0:90
Linked(sincePD>>NPD),45mapunits
2.DrawchromosomesinMeiosisItoexplain1dinthequestionabove.What
property(ies)ofmeiosisarealteredinthiscross.
Thereislikelytobeinterferencesothattherearenodoubleexchangesandonly
singleexchanges(chiamainterference).90%ofchromsomeswithsinglecrossover
and10%withnocrossover.
3.Youperformtetradanalysisontwonewlyisolatedmutants.Thetun1mutant
confersresistancetoTunicamycin.Theani1mutantconfersresistanceto
anisomycin.Inthetetradsyouobtain,youfind50parentalditypes.Youget10
tetradsthathaveonlytwoviablewild-typeprogenyand40tetradsthathaveonly
threeviableprogeny.
a. Whatarethelikelygenotypesofthethreeviableprogenyinthelastsetof
40tetrads?Theviablemeioticprogenyarelikelytobe
tun1;ANI1
TUNI;ani1
TUN1;ANI1
b. Howdoyouexplaintheinviablityinthecross?Thedoublemutant,tun1;
ani1islikelytobelethal.Thetwogenesarealsolinked.Thegene
symbolsneedtobeinitalicsorunderlinedtogettheanswercompletely
right.
4.YouisolateawildyeaststrainandcrossitbybothMATaandMATαlabstrains.
YoufindthatitmateswiththeMATαparent.Whenyoudissectthetetrads,youget
onlyabout5%viableprogeny.
a. Whatisthelikelyexplanationofthehighlevelofinviability?
Itislikelythatthewildyeaststrainisdiploidandthecrossisthentriploid
andgeneratesaneuploidyprogenythatareinviable.
b. Howwouldyoutestyourexplanationforparta?
5.YoudecidetobrewsomebeerbecauseyoucannotaffordtobuyUrbanChestnut
STLIPA.Yougetayeaststrain(LAB1)fromafriend.Whenyoumixitwithawild-
strain,thewildstraindies.Yougetasecondstrainfromadifferentfriend(LAB2)
andwhenyoumixeditwiththewildstrain,nodeathoccurredandyoumadesome
beer.
YoudecidetodeterminewhatisthecauseofthekillingphenotypeofLAB1.Youdo
acrossofLAB1byLAB2.Luckilytheyhavetherightmating-typealleles.You
dissect25tetrads.Foreachofthe100meioticprogeny,youmixthemwiththewild
strain.Youfindthatall100progenykillthewild-typestrain.
a. Howdoyouexplainthisresult?
Cytoplasmicinheritance.
b. Whatexperimentwillyoudototestyouridea?
6. Linear tetrads are useful for centromere mapping in Aspergillus and Neurospora. The
order can be used to map centromeres. The spores above the midline arise from one
meiosis I daughter and the spores below the midline arise from the other meiosis I
daughter. A rare Saccharomyces cerevisaie strain gives linear tetrads rather than
tetrahedral tetrads that have no order. The two phenotypes are shaded and unshaded
Below are tetrads in the order that they were found and scored. Determine if shaded gene
is linked to its centromere and what is the distance from the gene to its centromere if it
can be determined.
30
8
27
11
9
7
Yeast do not behave as Aspergillus. Rather the meiosis I daughter spindles are offset
So that the second and sixth class are showing reductional division. The rest show
equational division. So the gene is unlinked to the centromere as only 15 of the 89
tetrads show reductional division.
P.S TA thought the answer should be linked, and the distance is 19.
7. Describe the screen used to find autophagy mutants in yeast.
a.
How would you use multicopy suppression to find genes involved in
autophagy?
Norightanswer.
Whatphenotypewouldyouuse?
Useamulticopylibraryin2micronplasmidoruseahighlyexpressedpromoter.
Selectforphenotype.
Isolateplasmid,sequenceanddeterminegenesthatcanrescueinhighcopynumber.