NAME STUDENT ID MCB 140 1st Midterm Spring 2007 NAME Please print STUDENT ID REMINDERS 1 You have 50 minutes for the 150 point exam Exams will be collected at noon sharp 2 Print your name and ID on each page of the exam You will lose points if you forget to do this 3 There are 7 pages total including this cover page All pages must be turned in 4 Only the front of each page will be graded If you use the back of a page transcribe your answer to the space provided on the front of the page The exam is short but the questions are content laden i e well thought out answers are expected note this does not mean verbose just thoughtful Think before you start writing about the best way to express the point you wish to make Personal note from Prof Urnov I will grade my portion of the exam myself and would be grateful for somewhat more lucid prose and intelligible handwriting than one sometimes finds on midterms fdu Do not write below this line 2 30 4 30 5 30 6 30 7 30 TOTAL 150 Page 1 of 7 NAME STUDENT ID Question 1 30 points Shortly after the formal founding of the City of Berkeley on April 1 1878 you arrive there to study some botany Interested in the problem of inheritance you come across a paper in an obscure journal by a certain Gregor Johann Mendel The sweet pea seems too mundane for you so you pick the California poppy its bright orange flowers decorate many a hillside in Berkeley After much searching however you realize that all the poppies you can find are orange Undeterred you pick it as your model system Starting with a wild type i e available on the hillside population of uniformly orange colored California poppies describe the experimental sequence you would undertake to determine if petal color inheritance in this plant follows Mendel s First Law Your answer must take the form of a numbered list for each action 1 do this and that where appropriate please provide a justification so as to make sure that that and this happens Herman Muller invented the use of mutagens to induce mutations in the 1920s You are not ahead of your time in that respect All you have access to are some flowers from a hillside a patch of land the Sun a microscope and maybe some forceps brushes etc Page 2 of 7 NAME STUDENT ID Question 2 30 points A series of experiments by Thomas Hunt Morgan and his student Calvin Bridges on eye color inheritance in Drosophila provided strong experimental evidence that Mendel s particles of inheritance the genes lie on chromosomes A summary of crosses performed by Morgan is shown below and two questions about these experiments are on the next page See questions on next page please Page 3 of 7 NAME STUDENT ID Morgan himself wrote the following if my interpretation of the data is correct and the gene for white is on the X chromosome there should be two classes of females in the F2 generation namely What two classes of females is Morgan referring to 5 points Describe using modern genetic notation the experiment Morgan did to confirm this specific hypothesis and his data 10 points In apparent contradiction to his mentor s data on criss cross inheritance of eye color in Drosophila Calvin Bridges found a rare white eyed daughter offspring from a mating between a white eyed mother and a red eyed father He correctly interpreted this finding as evidence of nondisjunction in meiosis to yield an exceptional XXY female Describe in narrative form the two distinct forms of evidence Bridges provided in support of this hypothesis You do NOT have to describe every cross he did you are being graded on your ability to able to describe in a general sense and in a clear sentence or two Bridges s overall experimental approach to the problem 15 points Line of evidence 1 Line of evidence 2 Page 4 of 7 NAME STUDENT ID Question 3 30 points Alfred Sturtevant s name is rightly inscribed in the history of genetics for his drafting of the first ever genetic map His famous paper describing the data is entitled The Linear Arrangement of Six Sex Linked Factors in Drosophila as Shown By Their Mode of Association Linear that s a strong word Think about this for a couple of minutes and write a few wellworded sentences describing in general terms what evidence Sturtevant provided in support of the fact that genes are arranged in linear as opposed to some other order Yes he s right genes lie on chromosomes and a chromosome is a linear piece of DNA but that wasn t discovered until 1953 How did Sturtevant convince the reviewers that genes are in linear order 20 points The garden pea Pisum sativum has a diploid karyotype of 14 i e has only 7 linkage groups In his study of dihybrid crosses Mendel therefore was very likely to have picked two linked loci In fact for some of his two factor crosses he DID pick two linked loci which nonetheless yielded a perfect 9 3 3 1 ratio in a AaBb self cross How can this be 10 points Page 5 of 7 NAME STUDENT ID Question 4 10 points A and B are yeast genes immediately next to each other on chromosome II close to the telomere that is they are separated by a distance of 0 cM and far from the chromosome II centromere Consider a cross between two haploid yeast strains one A b and one a B What proportion of parental ditypes nonparental ditypes and tetratypes do you expect Question 5 20 points George Beadle and Edward Tatum mutagenized Neurospora strains and identified a haploid which harbored a single mutation making its growth dependent on vitamin B6 You get interested in this finding and repeat the experiment Surprisingly you identify a second haploid strain with an identical phenotype to that of Beadle and Tatum s mutant Your new Neurospora strain will not grow without vitamin B6 it accumulates the same chemical precursors to B6 as Beadle and Tatum s did and a cross between your mutant and a wild type strain indicates that a single locus is responsible for the phenotype in your strain You cross your strain to Beadle and Tatum s original mutant still available from the Stanford freezers to form a diploid You induce the diploid to undergo meiosis but rather than bothering with octad analysis you simply collect and grow 100 random haploid progeny All are viable on rich media You test the progeny for growth on media lacking B6 and find that 75 cannot grow under these conditions accumulating the B6 precursors the other 25 progeny can grow without B6 What do you conclude about your new mutant and about the enzyme controlling this step in B6 synthesis Page 6 of 7 NAME STUDENT ID Question
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