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Violation of Independent Assortment in Genetics: Bateson and Punnett's Chromosome Mapping

Explore the concepts of linkage, crossing over, and their effects on genotypic and phenotypic ratios in genetics based on the work of William Bateson and R.C. Punnett. Understand the non-independent segregation tendencies and partial gametic coupling observed in genetic crosses. Learn how to determine if genes are linked in coupling or repulsion through test crosses. Investigate the impact of crossing over on the number of possible gamete types.

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Violation of Independent Assortment in Genetics: Bateson and Punnett's Chromosome Mapping

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  1. OUTLINE 15 E. Violation of independent assortment 1. Bateson and Punnet 2. Linkage 3. Crossing over 4. Chromosome mapping 5. Effects of linkage and crossing over on genotypic and phenotypic ratios

  2. William Bateson and R.C. Punnett P = purple dominant to p = white L = long dominant to l = round P PPLL X ppll F1 all purple / long F2 PhenotypeNumberNumber expected Purple / long 284 215 Purple / round 21 71 Parental White / long 21 71 White / round 55 24 Tendency toward non-independent segregation - Partial gametic coupling

  3. Test cross F1 to double recessive: Parents PpLl X ppll Gametes PL pl Pl pL pl Expect 1:1:1:1 ratio of phenotypes Bateson and Punnett observed 7:1:1:7

  4. Test cross to determine if genes are linked in coupling or repulsion PL//pl x pl//pl Pl//pL X pl//pl Gametes 1/2 PL all pl 1/2 Pl all pl 1/2 pl 1/2 pL F1 1/2 PL//pl (purple, long) 1/2 (purple, round) 1/2 pl//pl (white, round) 1/2 (white, long) With independent assortment: PpLl x ppll expect 1:1:1:1

  5. P p p P L L l l = centrosome P: PL//PL X pl//pl F1: (PL//pl) p P p P L L l l

  6. Effects of crossing over on number of possible gamete types With x-over No x-over P p p P p p P P L L l l L L l l P p p P l L l L pL Pl PL pl

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