NAME: _____________________________________ STUDENT ID #: ______________________________ Page 1 of 7 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 _____ / 150NAME: _____________________________________ STUDENT ID #: ______________________________ Page 2 of 7 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.NAME: _____________________________________ STUDENT ID #: ______________________________ Page 3 of 7 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.NAME: _____________________________________ STUDENT ID #: ______________________________ Page 4 of 7 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 #2NAME: _____________________________________ STUDENT ID #: ______________________________ Page 5 of 7 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 well-worded 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)NAME: _____________________________________ STUDENT ID #: ______________________________ Page 6 of 7 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
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