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# Biology 3300- Multiple Loci

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School
Department
Biology
Course
BIOL 3300
Professor
Theresa Burg
Semester
Spring

Description
Biology 3300 Feb.3 , 2013 Multiple Loci: Linkage Linked Loci - On the same chromosome - Inherited as a ‘package’ - Fewer map units separating them, less recombination - Highly linked—closer on the chromosome - Alleles from two different loci inherit as a package Ex: - 25 chromosome: 12-AB 3-Ab 8-aB 2-ab - The two loci are in linkage equilibrium (look at frequency calculations) - The second example shows that the two loci are NOT in linkage equilibrium (B on A = 0.73, B on a = 0.9) What is the difference between the distributions of alleles in the previous two slides? - Allele frequencies do NOT differ - Haplotypes or ‘chromosome frequencies” do change o Haplotype: haploid genotype (ex: gametes, organelle genomes) D=g gAB abg Ab aB D = coefficient of linkage disequilibrium Linkage equilibrium D value should be 0 Left SIDE AB = 12/25 = 0.48 Ab = 3/25 = 0.12 aB = 8/25 = 0.32 ab = 2/25 = 0.08 D = g AB– abg Ab aB = (0.48*0.08) – (0.12*0.32) = 0.0384 – 0.0384 = 0 Right Side AB = 11/25 = 0.44 Ab = 4/25 = 0.16 aB = 9/25 = 0.36 ab = 1/25 = 0.04 D = g AB–ab g Ab aB D = (0.44*0.04) – (0.16*0.36) = 0.0176 – 0.0576 = -0.04 Loci are in linkage equilibrium if: 1. Frequency of B on chromosome with A = frequency of B on chromosome with a a. BA = 12/15 b. Ba = 8/10 2. Frequency of AB = frequency A* frequency B a. AB = 12/25, A*B = 0.6*0.8 3. D=0 (note: Dmax = 0.25) Why disequilibrium? - Selection on multilocus genotype - Genetic drift - Population admixture (2 genetically distinct populations accidentally put together) Individuals with
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