LECTURE3 - Lecture 3: Genetic mapping R ead in g (9 th ed...

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Lecture 3: Genetic mapping Linkage and how to detect it. Genetic maps are based on recombinant frequencies in the progeny of a testcross. Three-point testcrosses and gene order. Interference. Chi-square in linkage analysis. LOD scores. Reading (9th edition) pp. 102-145, 154-158
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Figure 4- 13c A map of the 12 tomato chromosomes
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0.08 = 80/1000 progeny are recombinants Recombination (crossing over)
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Recombinant frequency (RF) Recombinant frequency (RF) = Number of recombinants Total number of progeny (8% in this example, 80/1000) 1% recombinant frequency = 1 genetic map unit (m.u.) = 1 centimorgan (1 cM). Two unlinked genes have an RF of 50% (Why?)
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For linked genes, recombinant frequencies are less than 50 percent:
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Map distances are generally additive
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Linked alleles tend to be inherited together
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Chiasmata are the sites of crossing over
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Longer regions have more crossovers and thus higher recombinant frequencies:
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Recombinants of linked genes are produced by crossovers:
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Multiple crossovers can include more than two chromatids:
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Three point testcross
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Three point testcross 18.5% RF 13.2% 6.4%
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LECTURE3 - Lecture 3: Genetic mapping R ead in g (9 th ed...

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