# Post-Section C Answers Final.docx - Question 1 Pedigree...

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Question 1 Pedigree analysis of a large number of families has uncovered linkage between an autosomal recessive  disease (designated as Disease Locus or DL) and a SNP marker (T) on chromosome  4.  Previous studies have been conducted that measured the linkage between marker T and another nearby SNP marker (S).  The results of these two studies are shown to the right on this LOD score vs. theta plot: a)  ( 20 pts ) Based on these results, indicate the two possible maps that can be drawn for the relative  positions of DL and the two SNP markers on chromosome 4.  Be sure to indicate the best map  distances between each of the three genes/markers. Between S and T: 5 mu Between DL and T: 15 mu       Map 1:     -----------DL--------------(10 mu)-------------------S-----(5 mu)------T----------------                 |-----------------------------(15 mu)----------------------------| Map 2:     -----------DL----------------(15 mu)------------------T-------(5 mu)----S-------------                   |----------------------------(20 mu)------------------------------| 10 points per map. See below for breakdown

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Grading: 1a) 20 pts total For each of the two maps (order): (+3 points each for correct order) For each of the two maps (distances): +7 points each for correct distances o +3 points for one correct distance between two loci o +3 points for another correct distance between two loci o +1 point for the third correct distance o Only docked off one point per map for students who failed to include a third distance (namely, the distance between the two outer loci) because this is a common mistake and is due to not reading the question carefully rather than not understanding the biology Note: Having numbers slightly different than the distance provided in the answer key is acceptable (because the graph wasn't high resolution) Note: Saying 0.15 cM instead of 15 cM and similar mistakes resulted in Minus 2 points per map
In order to distinguish between these two map orders, a search was made for particularly informative pedigrees.  An example of one such pedigree is shown below:       T 1  S 2  DL+                           T 2 S DL b)   (10 points)  Where possible, identify each individual who has inherited a recombinant set of the  three genes from one of its parents.  Circle these individuals and identify the recombinant set of  alleles by writing it underneath their symbol.  For the disease locus, use  DL  to denote the disease  allele and  DL+   to denote the wild-type allele. Grading 1b): (worth 10 points total) Circling individuals: 4 points total o +2 points for each correct circling of a recombinant individual as shown in key above. o Minus 2 points for each circling of a non-recombinant individual (0 points min.) Writing of Recombinant set of alleles: 3 points each for 6 points total o +3 points for writing out the correct recombinant set of alleles.

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• Fall '09
• Distance, gene D, Swingnose crossing, Dantian

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