Name:___________________________________ Section:_____7.012 Fall 20037.012 Problem Set 3Question 1You have two pure-breeding colony of mice. Colony I mice have black fur and long tails,Colony II mice have golden fur and short tails.You cross mice from each of these colonies.F0black fur andlong tailsXgolden fur andshort tails⇓F1Brown fur andlong tailsa) Predict genotypes for the mice shown in the cross above. Define your notation.i) black fur and long tails:ii) golden fur and short tails:iii) Brown fur and long tails:b) You mate a male and a female from the F1 generation. Given your prediction in (a), whatgenotypes and phenotypes do you see in the F2 generation, and in what ratios?Please print out this problem set and record your answers on the printed copy. Answers tothis problem set are to be turned in at the box outside by 4:10 Wednesday, October 1.Problem sets will not be accepted late. Solutions will be posted on the web October 2,2003.MIT Biology Department7.012: Introductory Biology - Fall 2004Instructors: Professor Eric Lander, Professor Robert A. Weinberg, Dr. Claudette GardelName:___________________________________ Section:_____7.012 Fall 2003FIGURE 1:ABCDEFGHXYAFABFA CEFGHYABCDEFGHXYplate 1plate 2plate 3plate 4plate 5rich mediumminimal medium + pheminimal mediumminimal medium + PEPrich mediuma) Plate 1 is the original rich medium plate that the mutagenized cells were grown on. It isstandard practice for the last plate in a series of replica plates to have the same growthmedium as the original plate. What purpose might this serve?b) You obtain some phe- colonies in this manner. Identify the colonies from FIGURE 1 that arephe-c) You notice that some colonies do not grow on plates containing minimal medium +phenylalanine (plate 2). Identify these colonies and give one possible explanation for thegrowth behavior of these colonies.d) This strategy for isolating phe- mutants works well so you repeat the mutagenesis andreplica plating experiment to isolate more phe- mutants. You then perform acomplementation test on these phe- mutants.i) What is a complementation test?ii) What is the purpose of a complementation test?Name:___________________________________ Section:_____7.012 Fall 2003Question 2, continuedIn the table below, a (+) indicates that the diploid created grows on minimal media, a (-)indicates that the diploid fails to grow on minimal media.m1m2m3m4m5m6m7m8m9m10m1--++++-+++m2--++++-+++m3++-+++++++m4+++-+++++-m5++++-+++-+m6+++++-+-++m7--++++-+++m8+++++-+-++m9++++-+++-+m10+++-+++++-ii) Assign the mutants 1-10 into complementation groups.e) You also characterize your mutants based upon which of the intermediates accumulatesm2: accumulates Xm3: accumulates Zm4: accumulates PEPm5: accumulates Ym6: accumulates WBased on the above data, you predict thati)m1 has a mutation in gene______ii)m2 has a mutation in gene______iii)m3 has a mutation in gene______iv)m4 has a mutation in gene______v)m5 has a mutation in gene______Name:___________________________________ Section:_____7.012 Fall 2003Question 3Replica plating has been used to address profoundly important questions in bacterial genetics.For example, in the 1940's there was much debate regarding the issue of whether or notmutants pre-exist in a population of bacteria. Researchers observed that when they inoculatedwild type (penS) bacteria onto growth medium containing penicillin, and thus selected forbacteria that had mutated to become penicillin resistant, a small fraction (~10-6) of cells wouldalways grow. Thus, penR colonies had arisen from a penS population. There were two modelsfor this:Model A: "Directed Mutations" One group of researchers argued that these mutants originatedas a result of the selective pressure. Their line of reasoning was that the bacteria can sense theneed to grow on penicillin and that a small fraction of them successfully mutate in a directedmanner so that they become penR.Model B: "Pre-existing Mutations" A second group of researchers argued that penR mutantspre-existed within the wild type population before ever coming into contact with penicillin;thus, (they argued) penicillin doesn't direct mutations, it simply reveals mutants.Replica plating provided a rapid means for testing these two hypotheses. The following is asimplified version of the experiment. Plate 1 contains a "lawn" of cells (a solid layer of cellspacked together), all of which are the offspring of a single, wild type cell. About 5 X 106 cellswere spread on a plate, and after a day of growth, they formed a lawn containing about 109cells. Plate 1 was used as the master plate that was replicated onto plates 2, 3, 4, and 5.The distribution of colonies on plates 3, 4, and 5 is identical.a) Which of the two hypotheses (directed mutations or pre-existing mutations) does this resultmore strongly support. Explain your reasoning.Name:___________________________________ Section:_____7.012 Fall 2003Question 4Shown below is a diagram of a replication fork in a double-stranded (ds) DNA molecule foundin a prokaryotic cell. Each DNA strand (A and B) serves as a template for polymerization byDNA polymerase, resulting in the formation of a newly synthesized "daughter" DNA strand.Replication forkmoves in this direction5’3’3’5’strand Astrand Ba)i) On which template strand (A or B) would there be continuous replication by DNApolymerase? What is this newly synthesized daughter strand called during DNAreplication?ii) On which template strand (A or B) would there be discontinous replication by DNApolymerase? What is this newly synthesized daughter strand called during DNAreplication?iii) Chemicals that inhibit the enzyme DNA ligase will primarily affect synthesis on oneof the two template strands (A or B). Explain on which template strand (A or B)polymerization will be primarily affected and why this occurs.b) There are inaccuracies in the DNA molecule shown below.!!! 1 5 10!!!5' A G T C C G A U G C 3' | | | | | | | | | |!!!5' T C A G G C T A T G 3'i) Name three things that are wrong in the above DNA sequence.ii) What type of chemical interaction is indicated by a "|" in the above diagram? Whathappens to these interactions during DNA replication?Name:___________________________________ Section:_____7.012 Fall 2003c) Shown below is the structure of a monomer used in nucleic acid synthesis.αβγ OHH HOCH2OPOPOPHONNNNNH2O O OH HO–O–O–O–i) Would this monomer be used to form part of an RNA
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