Topic5.pdf - Topic 5 Linkage and Mapping 1 Investigate...

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Topic 5: Linkage and Mapping 1. Investigate patterns of inheritance among linked genes, that is when alleles are inherited together more than 50% of the time and explore how physical proximity in the genome affects this pattern. 2. Quantify genetic distance between loci using the frequency with which two alleles are inherited separately, using either two-point or three-point crosses. Create linkage maps by combining this data across experiments. 1
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Topic 5: Big Question How does proximity between genes affect independent assortment?
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RrYy X RrYy Mendel showed traits are inherited independently 3 Why are there exceptions to this rule? 1. Chromosomes assort independently 2. Crossing over means alleles on the same chromosome may be shuffled
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One pair of homologous chromosomes ab AB x ab ab 4
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One pair of homologous chromosomes ab AB x ab ab a a A b b B B B b a a a A b b b B 5
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Non-independent Assortment Bateson, Saunders, Punnett (1905) Purple color > Red color Long pollen > short pollen 6
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Non-independent Assortment Phenotyp e Observed # Observed Ratio Expected Ratio Purple, long 284 12 9 Purple, short 21 1 3 Red, long 21 1 3 Red, short 55 2.6 1 7
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Terminology linked genes- genes that are inherited together, may be physically close linkage groups – a series of genes that are linked, may represent all or part of a chromosome. genetic recombination- the product of crossing over, recombinant chromosomes carry new combinations of alleles. linkage map or genetic map– a genome wide analysis of recombination results in a map of the relationship between genes. 8
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Non-independent Assortment Phenotyp e Observed # Observed Ratio Expected Ratio Purple, long 284 12 9 Purple, short 21 1 3 Red, long 21 1 3 Red, short 55 2.6 1 9
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Notation for unlinked and linked genes Unlinked: if linked: 10
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