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Epistasis

Epistasis. Definition. Epistasis is a form of gene interaction in which one pair of alleles (gene) masks the phenotypic expression of another. Epistasis is a form of polygenics The new phenotype is really the “absence” of the usual phenotype. It can result in albinism.

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Epistasis

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  1. Epistasis

  2. Definition • Epistasis is a form of gene interaction in which one pair of alleles (gene) masks the phenotypic expression of another. • Epistasis is a form of polygenics • The new phenotype is really the “absence” of the usual phenotype. It can result in albinism.

  3. Epistatic versus Hypostatic • The alleles that are interferring or masking the effect are called epistatic alleles • The alleles whose effect is being interferred with or masked are called the hypostatic alleles.

  4. Recessive or Dominant? • Epistasis can be described as either recessive epistasis or dominant epistasis. • Let’s look at an example of recessive epistasis….

  5. Labs (the dogs!) • Fur color in Labs is controlled by two separate genes. • Fur color is a polygenic trait! Gene 1: Represented by B : Controls color Gene 2: Represented by E : Controls expression of B

  6. Labs • If a Lab has a dominant B allele, they will have black fur. • If they have two recessive alleles (bb) they will have brown fur.

  7. Labs • If a lab receives at least one dominant “E” allele, they will remain the color that the “B” allele coded for. • Either black of brown • However, if a dog receives a pair of homozygous recessive “e” alleles, they will be golden regardless of their “B” alleles! • This would be considered “Recessive Epistasis”

  8. Labs • BBEE and BbEe --> Black lab • bbEE and bbEe --> Brown lab • BBee, Bbee, or bbee --> Golden lab • Recessive Epistasis

  9. Try this cross… • You have decided to cross your golden lab (bbee) with the neighbor’s black lab (BbEe). What color pups will they have? (Shortcut?) • Yup…..you have to do a dihybrid cross.

  10. bbee x BbEe • FOIL: be • FOIL: BE, Be, bE or be • Genotypes of F1 generation: BbEe; Bbee; bbEe; bbee • Pups phenotypes:Black (25%); brown (25%) • and golden (50%)

  11. Dominant Epistasis • Let’s have a look at dominant epistasis… • Squash fruit color is controlled by two genes. • Gene 1 is represented by a W • Gene 2 is represented by a G

  12. Squash Fruit Color • Genotypes and Phenotypes: • W_/G_ white • W_/gg white • ww/G_ green • ww/gg yellow

  13. Squash Fruit Color • Which type of epistasis is represented here? • How do you know? Dominant Epistasis Because every time a dominant W allele shows up in a squash genotype, the squash fruit color is white.

  14. Dominant Epistasis • Epistatic Alleles? • WW • Hypostatic Alleles? • G alleles

  15. Try this cross…. • Cross a green squash (wwGg) with a white squash (Wwgg). • What color are the offspring?

  16. Wwgg x wwGg • FOIL: Wg or wg • FOIL: wG or wg • F1 generation genotypes: • Phenotypes:

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