Life Sci 1b � Lecture 8

Life Sci 1b � Lecture 8 - Life Sci 1b Lecture 8...

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Life Sci 1b – Lecture 8 26/02/2008 10:09:00 Midterm Reviews: Fri 4-6 SC-D, Thu 3-5 SC-C (redundant) Medterm March 4 (next Tuesday) bring calculator, cribsheet (1 page, front and back) Sections meet for GDP Intro first this week Midterm location:  Geological Museum #100 Help sessions, office hours, etc Outline Recombination Genetic mapping A closer look at human chromosomes (Genetic mapping) Three-gene cross (three-point) switches the middle of 3 genes Data remember, no crossing over in male Drysophila Analyze the data to determine   o 1. The linkage phase of the alleles   o 2. The correct gene order 
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o 3. The map distance between each outside marker and the middle  marker   o 4. The frequency of recombination between the outside markers Linkage phase Most frequent classes of progeny are nonrecombs. Gene order Least frequent classes of progeny are double recombs. The middle marker is flipped, so you can figure out the gene order In this example, gene C is in the middle Retabulate the data Correct order and linkage phase Write parental reciprocals at the top, recombinant reciprocals in the middle (2  pairs), double recombs at the bottom Map distance (cM) and frequency of recombination Because of double crossovers, estimating map distance from shorter distances  is more accurate than measuring them from longer  distances. Calculation: number of recombinants out of total (here, 77/1000 for CB and 
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Life Sci 1b � Lecture 8 - Life Sci 1b Lecture 8...

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