Linkage & Mapping Lecture 11 and 12

Linkage & Mapping Lecture 11 and 12 -...

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Rare Diseases: 80% are Genetic, 75% affect children http://www.rarediseaseday.org/article/what-is-a-rare-disease
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Chapter 7 Linkage and Mapping Drosophila
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3.11 p.61 Mendel’s Independent assortment ROUND/wrinkled YELLOW/green 9 R_Y_ 3 R_yy 3 rrY_ 1 rryy Independently Segregating Gene Ratio
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"Nonindependent" Assortment 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
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purple color dominant over red color long pollen dominant over short pollen 7.3 p.162 Bateson, Saunders, Punnett (1905) Nonindependent Assortment
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7.3 p.162 284 12 > 9 parental 21 1 < 3 21 1 < 3 55 2.6 > 1 parental # ratio ratio Observed Independent
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"Nonindependent" Assortment Chi square was off the charts = 132 Noticed that both parental phenotypes were expressed at higher numbers in the F2 progeny “coupling” perhaps some physical connection between parental alleles
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Terminology linked genes linkage groups genetic recombination linkage map Chromosome 1 Chromosome 2 A B C D E a b c d e
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An aside about notation for linked genes AABB x aabb if linked A B a b A B a b X A B a b A B a b A B/a b
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Linked vs. Unlinked Two genes A and B test cross with heterozygote reveals if genes are linked or assort independently non linked 1 parental : 1 parental : 1 recombinant :1 recombinant 50% are nonrecombinant progeny 50% are recombinant progeny linked - no ratios predictable But more parental combinations (nonrecombinant) progeny than recombinant % of recombinant determined by amount of crossing over that occurs
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7.5 p.165 50% parental 50% recombinant 100% parental 0% recombinant e.g. different chromosomes
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Crossing over between homologous chromosome Meiosis I 2.16 p.30
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7.7 p.167
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7.7 p.167
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Coupling and Repulsion In studying linked genes, the arrangement of alleles is not critical, but affects recombinant Non-linked – M and D phenotypes segregate independently Linked - two possible arrangements M D m d Coupling (or cis) M d m D Repulsion (or trans) M and D phenotypes tend to stay together M and D phenotypes tend to stay apart
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How "linked" is linked? Use test cross with heterozygote for
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Linkage &amp;amp; Mapping Lecture 11 and 12 -...

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