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Understanding Genetic Inheritance and Phenotypic Ratios with Linked Genes and Epistasis

Explore concepts like independent assortment, crossing over, and chromosome mapping to grasp how gene interaction, linkage, and epistasis influence genotypic and phenotypic traits. Study cases of pleiotropy and violation of complete expression, observing diverse phenotypes in organisms due to genetic variations. Delve into the effects of crossing over on gamete types and learn about phenotypic plasticity in response to environmental factors.

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Understanding Genetic Inheritance and Phenotypic Ratios with Linked Genes and Epistasis

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  1. OUTLINE 16 E. Violation of independent assortment 3. Crossing over 4. Chromosome mapping 5. Effects of linkage and crossing over on genotypic and phenotypic ratios F. Pleiotropy G. Violation of complete expression 1. Gene interaction - epistasis 2. Consequences penetrance expressivity H. Phenotypic plasticity

  2. 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

  3. 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

  4. 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.

  5. Alfred H. “Hot Dog” Sturtevant

  6. 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

  7. Fig 15.6

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

  9. 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 heterozygous • 7. Each trait is controlled by a different set of factors

  10. Pleiotropy: The same locus influences coat color and crossed eyes in felines

  11. Fig 14.11 Effect of epistasis on phenotypic ratios of a dihybrid cross C= pigment c = none B = deposition of lots of pigment (black) b = less deposition (brown) If cc, fur is white regardless of genotype at B locus

  12. Predator absent Predator present Phenotypic plasticity in Daphnia

  13. Crayfish predator Sunfish predator Snail prey

  14. A full sib raised with crayfish A snail raised with fish

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