Lecture Notes 9

Lecture Notes 9 - Lecture 9 2/5/2008 Biosc 0350 Genetics...

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Lecture 9 2/5/2008 1 Biosc 0350 Genetics Lecture 9 - Mapping in eukaryotes (2) Recombination of genes on same chromosome Two-factor crosses to order genes Three-factor crosses to order genes Gametes produced by trihybrid Double crossovers indicate order Calculating map distances Interference Linkage maps 2/5/08 Martens. Biosc 0350, University of Pittsburgh 2 A “through the microscope” look at recombination of genes on the same chromosome? How? When? Who’s involved? What structure marks recombination? Where? Hartwell et al , 3rd ed. Figure 5.7
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Lecture 9 2/5/2008 2 2/5/08 Martens. Biosc 0350, University of Pittsburgh 3 Terminalization: chiasmata resolve during anaphase I Reciprocal exchange Result: 4 haploid products • two parental • two recombinants A “through the microscope” look at recombination of genes on the same chromosome? Hartwell et al , 3rd ed. Figure 5.7 2/5/08 Martens. Biosc 0350, University of Pittsburgh 4 Reciprocal exchanges between homologous chromosomes are the physical basis of recombination Fig. 5.6 ~1930’s - Stern (Drosophila); Creighton and McClintock (corn) • used unusual genetic structures to observe genetic exchange occurs by breaking and rejoining of the chromosomes Stern • 2 X-linked genes - carnation eyes (car) - kidney-shaped eyes (bar) Hartwell et al , 3rd ed. Figure 5.6
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2/5/2008 3 2/5/08 Martens. Biosc 0350, University of Pittsburgh 5 Recombination frequencies for pairs of genes reflect distance between them. A B a b A B a b A B a b A B a b A B a b A B a b RF=50% RF=32.8% RF=1.1% >50 map units 32.8 map units 1 m.u 1 % RF = 1 map unit (m.u) = I centimorgan (cm) 2/5/08 Martens. Biosc 0350, University of Pittsburgh 6 Mapping: Determining relative positions of genes along a chromosome 1) Two-point testcrosses: Comparisons help establish relative gene positions. Hartwell et al , 3rd ed. Figure 5.9
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Lecture Notes 9 - Lecture 9 2/5/2008 Biosc 0350 Genetics...

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