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Gene Interaction and Epistasis

Gene Interaction and Epistasis. We know that many characteristics are passed on through genes. Most of these characteristics are not passed on through one gene with only two alleles. Most are polygenic where their traits are caused by a number of different genes.

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Gene Interaction and Epistasis

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  1. Gene Interaction and Epistasis

  2. We know that many characteristics are passed on through genes. • Most of these characteristics are not passed on through one gene with only two alleles. • Most are polygenic where their traits are caused by a number of different genes. • Or they are caused by multiple alleles where a single gene has more than two possible alleles. • This can make inheritance very complicated.

  3. Gene Interaction This is when the alleles of more than one gene affect each other. A good example of this is the comb shape of a chicken Pea Comb Walnut comb Rose comb Single comb

  4. It was found that two genes were responsible for the four different comb shapes. • For one gene, the dominant allele P gives a pea comb. • The dominant Allele for the other gene R, gives a rose comb. • When both dominant alleles appear together they produce a walnut comb. • If the dominant alleles aren’t present then a single comb is produced. What comb shape would these genotypes produce: PPrr ppRR PpRr ppRr Pprr pprr

  5. Epistasis Epistasis is when one gene affects or alters the expression of another. A good example is coat colour in cats: The agouti gene causes a striped effect in the cat’s fur, if the gene isn’t present the cat will have a solid coat colour

  6. Agouti alleles = A and a AA, Aa codes for an agouti coat aa codes for a solid colour coat The tabby coat pattern has 3 possible alleles: T, TB, and tb TT or Ttb produces a mackerel tabby coat pattern.

  7. tbtb is recessive and produces a blotched tabby coat. TBT, TBTB, or TBtb produces a more freckled appearance:

  8. However: Without at least one dominant agouti allele, none of these tabby characteristics will appear in the cat’s phenotype. Lets look at some possible genetic diagrams for this : AAtbtb with aaTT AaTTB with aaTT AaTtb with AaTTB

  9. Be careful not to confuse epistasis with dominance. Dominance occurs between two alleles of the same gene. Epistasis occurs between two genes coding for different characteristics.

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