Lect 12-2018.pptx - Chapter 5 Linkage and Mapping in...

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Chapter 5 Linkage and Mapping in Eukaryotes BIOL203- Lecture 12 Thomas Hunt Morgan (1866-1945) Prof. of Zoology Columbia University (1904-1928) Ph.D. students: C. Bridges, A. Sturtevant, H. Muller,… Chromosomal inheritance of traits, linkage, sex-linkage, genetic mapping mutational analysis ( white ), mutagenesis, etc.
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Chapter 5 Linkage and Mapping in Eukaryotes BIOL203- Lecture 12 IMPORTANT POINTS: -genes close to one another on the chromosome do not assort independently: they are linked -this means they often segregate together in meiosis -linked genes can be separated by recombination in meiosis: they will then segregate away from each other -this is a rare event -the further away two genes are from each other, the higher the frequency of recombination -if detected by phenotypic analysis: recombination is a measure of distance between two genes
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Unlinked genes Figure 5.1 Two unlinked genes (or markers, or mutations): assort independently and randomly: 25% of each genotype, 50% parental, 50% non-parental
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Genetic linkage: on same chromosome arm Figure 5.1 Two linked genes (or markers, or mutations): Segregate together unless they are separated by recombination The parental genotypes (non-recombinants) far exceed the non-parental genotypes HALLMARK OF LINKAGE: SIGNIFICANT PROPORTION OF PARENTAL GENOTYPES OVER 50%
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The degree of linkage varies and depends on distance Figure 5.2 The proportion (%) of recombinant types (non-parental) depends on the physical distance between the genes on the chromosome
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