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Unformatted text preview: 1 PRACTICE GENETICS QUESTIONS FOR MIDTERM II, Spring '10 KEY 1. A New York Times article entitled Mice Ignore Mendels Laws (5/26/06), pointed out that anomalous findings are often dismissed in science, because researchers believe the experiment must have come out wrong or that it is not worth the effort of tracking down the cause. Describe one possible experiment that Mendel himself might have done with his garden peas where he might have dismissed the results because he could not reconcile them with his theory of discrete factors (alleles of genes) that obeyed the law of equal segregation. (In your answer be sure to explain why Mendel might have considered the results in the experiment you describe anomalous.) He probably crossed two lines with different alleles for a trait that showed incomplete or co-dominance . That would have produced offspring with blended or mixed traits that would be hard to reconcile with discrete genes. It would also have been hard to discern the equal segregation of the alleles if the trait was quantitative and controlled by more than one gene. Since most traits behave in the non-Mendelian fashion, its hard to believe that he didnt see some those sort of results. 2. Although a single diploid individual can carry only two different alleles for a given gene, more than two alleles may still occur in a population. One example is the A, B, and O alleles for antigen proteins on the surfaces of human red blood cells. Another example is a gene that controls coat color in rabbits. Four alleles are found: C (gray), C ch (chinchilla, silver-gray), C h (Himalayan, white with dark tips of the extremities), and c (albino white). The order of dominance of these alleles is: C > C ch > C h > c . a) If a gray rabbit of genotype C c is bred with a chinchilla rabbit of genotype C ch C h , what phenotypes are possible in the progeny, and in what expected ratios? Show your work. Cc x C ch C h | V C C ch C C h C ch c C h c = (2) gray : (1) chinchilla : (1) Himalayan b) Is it possible to do a single cross that would yield a litter of baby bunnies with all four possible coat colors represented? If so, show the genotypes of the parents. If not, explain why not. (2 pts.) No, because in order to get the albino white bunnies (genotype cc), each parent must carry the c allele. Thus only a maximum of three different alleles can be represented between the two parents, but all four alleles are needed to produce all four phenotypes. 3 . You and a friend are bird breeders. You cross true breeding green-feathered birds with true breeding white-feathered birds and you get F 1 green-feathered birds. You then mate the F 1 birds with each other and are surprised to get: 17 green-feathered 7 yellow-feathered 6 blue-feathered 2 white-feathered You think that this is a case of multiple alleles in one gene for feather color, because you see more that two types of feather colors. Your friend thinks that this is a case of two interacting genes affecting a...
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