6-Linkage, Mapping and Recombination

6-Linkage, Mapping and Recombination - Linkage, Mapping and...

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Linkage, Mapping and Recombination Chapter 7 Terminology o linked genes o linkage groups o genetic recombination o linkage map "Nonindependent" Assortment o Bateson, Saunders, Punnett (1905) crossed sweet peas that were known to be homozygous for certain traits red flowers and short pollen purple flowers and long pollen • figure 7.3, page 162 o Chi square was off the charts! o Noticed that both parental phenotypes were expressed at higher numbers in the F2 progeny “couping” perhaps some physical connection between parental alleles A Physical Explanation o Thomas Hunt Morgan (again!!) o two recessive genes in fruit flies purple eye ( pr ) vestigial wing ( vg )
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An aside about notation for linked genes o AABB x aabb How "linked" is linked? o Use test cross with heterozygote for two linked genes o Count progeny to determine the frequency of recombinants Alfred Sturtevant (while an undergraduate in Morgan’s lab) suggested that the RF be used as a quantitative index of the linear distance between two genes. 1 map unit = 0.01 RF = 1% recombination Linked vs. Unlinked 0. Two genes A and B 0. test cross with heterozygote reveals if genes are linked or assort independently 1. non linked - 1:1:1:1 0. 50% are nonrecombinant progeny 1. 50% are recombinant progeny 2. linked - no ratios predictable 2. most are nonrecombinant progeny 3. % of recombinant determined by amount of crossing over that occurs see 7.5, p.165, 7.7 p. 167 Coupling and Repulsion o In studying linked genes, the arrangement of alleles is critical o Non-linked - AaBb
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6-Linkage, Mapping and Recombination - Linkage, Mapping and...

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