Name key 7 03 Exam Three 2005 KEY Name Exam starts at 11 05 am and ends at 11 55 am There are 8 pages including this cover page Please write your name on each page Only writing on the FRONT of every page will be graded You may use the backs but only as scratch paper Question 1 17 pts Question 2 45 pts Question 3 20 pts Question 4 18 pts TOTAL out of 100 1 Name key 1 17 pts You are studying the expression of the yeast gene ProA that is necessary for the synthesis of the amino acid proline ProA is normally expressed only when the cell is lacking supplemental proline in the growth medium You isolate two haploid yeast strains ProB and ProC that misregulate ProA expression You mate a ProB haploid strain to a wild type haploid strain The resulting diploid expresses ProA properly You mate a ProB haploid strain to a ProA haploid strain The resulting diploid expresses ProA properly You mate a ProA ProC haploid strain to a ProC haploid strain The resulting diploid expresses ProA when proline is present in the growth medium You mate a ProC haploid strain to a ProA haploid strain The resulting diploid expresses ProA properly You mate a ProB ProC haploid strain to a wild type haploid strain The resulting diploid expresses ProA properly You induce sporulation of this diploid and examine 40 tetrads 30 of those 40 each contain two spores that do not express ProA when proline is absent from the growth medium one spore that expresses ProA when proline is present in the growth medium and one spore that expresses ProA properly a 6pts Classify the ProB mutation by its genetic properties cis vs trans constitutive vs uninducible dominant vs recessive Trans recessive uninducible Trans You mate a ProB haploid strain to a ProA haploid strain The resulting diploid expresses ProA properly This means that the A and B mutations complement each other and are thus in different genes This means that B must act in trans to A Recessive You mate a ProB haploid strain to a wild type haploid strain The resulting diploid expresses ProA properly This means B is recessive Uninducible The only mutant phenotypes you see when you sporulate a diploid that contains both the B and C mutations are constitutive and uninducible C gives constitutive so B must give uninducible b 6pts Classify the ProC mutation by its genetic properties cis vs trans constitutive vs uninducible dominant vs recessive Trans recessive constitutive Trans You mate a ProC haploid strain to a ProA haploid strain The resulting diploid expresses ProA properly This means that the A and C mutations 2 Name key complement each other and are thus in different genes This means that C must act in trans to A Recessive You mate a ProC haploid strain to a ProA haploid strain The resulting diploid expresses ProA properly This means C is recessive Constitutive You mate a ProA ProC haploid strain to a ProC haploid strain The resulting diploid expresses ProA when proline is present in the growth medium This means that a cell that has a functional copy of A but has no functional copies of C expreses ProA even when it is not supposed to i e when the cell already has proline available to it c 5pts If you a drew a linear pathway showing the regulation of ProA which function would you place closer to ProA ProB or ProC ProB When you sporulate a diploid that was produced from a mating of B C to B C you see mostly tetratypes You know they are tetratypes because the types of spores do not come in pairs There are three types of spores Each tetratype contains two spores that do not express ProA when proline is absent from the growth medium uninducible one spore that expresses ProA when proline is present in the growth medium constitutive and one spore that expresses ProA properly inducible A tetratype resulting from this mating would contain the spores GENOTYPE PHENOTYPE B C uninducible B C constitutive B C inducible B C NOT KNOWN PREVIOUSLY The spore of unknown phenotype must be the double mutant and it shows the single mutant phenotype of B uninducible so B must be more downstream in the pathway i e closer to the reporter gene 2 45 pts You are studying the transcriptional regulation of a mouse gene called Stringy This gene is normally only expressed in tail cells due to the presence of a tailspecific inducer molecule in these cells You have isolated two true breeding mutant strains of mice that do not spatially regulate the expression of the Stringy gene properly The strains of mice that you have and their corresponding phenotypes are listed in the table below Genotype of mouse Wild type Phenotype of mouse Stringy expressed only in tail 3 A A B B Name key Stringy not expressed anywhere Stringy expressed in all cells in the body When you cross mice that are B B to mice that are deficient in Stringy the resulting mice only have Stringy expressed in the tail When you cross mice that are B B to mice that are A A and then cross the resulting F1 mice to each other you get a genotypic ratio in the F2 that indicates that the A and B loci segregate independently of each other You inject a piece of DNA containing the A allele of the A gene into a fertilized egg produced by the mating of two true breeding B mice You then transfer this injected fertilized egg into a pseudopregnant mouse The mouse that is born does not express Stringy in any cells in its body a 6pts Classify the A mutation by its genetic properties cis vs trans constitutive vs uninducible dominant vs recessive Trans dominant uninducible Trans dominant and epistatic to B You inject a piece of DNA containing the A allele of the A gene into a fertilized egg produced by the mating of two truebreeding B mice You then transfer this injected fertilized egg into a pseudopregnant mouse The mouse that is born does not express Stringy in any cells in its body The phenotype you are seeing in this A A A B B mouse is the phenotype of A not the phenotype of B which is constitutive This tells you three things 1 A is dominant This mouse has 3 copies of A and two of them are wild type and yet you see the mutant phenotype Thus A must be dominant 2 A can affect Stringy in trans A must have randomly integrated into the mouse genome and yet it can influence Stringy expression This means that A is capable of acting on Stringy from a distance 3 A is downstream of B This mouse is a double mutant A and B B The phenotype shown is that of A Thus A must be downstream of B in the pathway Uninducible Line 2 of the chart b 6pts Classify the B mutation by
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