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OUTLINE 15 E. Violation of independent assortment 1. Bateson and Punnet 2. Linkage

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. Application of Mendel’s Rules assumes:

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OUTLINE 15 E. Violation of independent assortment 1. Bateson and Punnet 2. Linkage

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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. Application of Mendel’s Rules assumes: • 1. One allele completely dominates the other • 2. All genes have 2 allelic forms • 3. All traits are monogenic (affected by only one • locus) • 4. All chromosomes occur in homologous pairs • 5. All genes assort independently • 6. An allele is completely expressed when either • dominant or homozygous • 7. Each trait is controlled by a different set of factors

  3. Bateson and Punnett also studied peas: Flower Color: P = purple p = white Pollen seed shape: L = long l = round True Breeding lines: PPLL x ppll P PpLl F1 Phenotype Number Exp Ratio Exp Number Purple long 284 9 215 Purple round 21 3 71 White long 21 3 71 While round 55 1 24 What is going on????

  4. 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 Some gamete types more common that others…but why???

  5. Hair Color Eye Color Eye Color Hair Color Independent loci Linked loci

  6. 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

  7. Linked genes sorted on chromosomes Explained why linkage not perfect Thomas H. Morgan

  8. 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

  9. 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

  10. Alfred H. “Hot Dog” Sturtevant

  11. Test cross F1 to double recessive: Parents PpLl X ppll PL//pl X pl//pl Gametes PL pl PL parental (7) Pl pl parental (7) pL pL recombinant (1) pl Pl recombinant (1) Expect 1:1:1:1 ratio of phenotypes Bateson and Punnett observed 7:1:1:7 2/16 = 12.5% recomb.

  12. L P 12.5 map units 5 units A L How do we know if it’s P- A - L , or P - L- A? If x-over frequency between P and A is 7.5% then: P A L 7.5 map units 5 map units If x-over frequency between P and A is 17.5% then: P L A 12.5 map units 5 map units

  13. sa (antennae mutation) b 9 cn 17 9.5 vg be (eye color) Fig 15.7

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