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A-Level Biology OCR A

Genes Epistasis Enzymes Produce Color Precursor Consecutive Formed

Epistasis occurs when the expression of one gene masks the effect of another gene. In an example involving enzymes needed for pigment production, if a gene coding for a crucial enzyme isn't expressed, it halts the enzyme cascade and prevents the final product from forming, thereby masking the effect of downstream genes.

L'épistasie se produit lorsque l'expression d'un gène masque l'effet d'un autre gène. Dans un exemple avec des enzymes nécessaires à la production de pigments, si un gène qui code pour une enzyme essentielle n'est pas exprimé, cela interrompt la cascade enzymatique et empêche la production du produit final, masquant ainsi l'effet des gènes suivants.

Front Describe how epistasis can occur.
Back Epistasis (example):
  • Enzymes are required to produce a pigment responsible for color
  • Genes are needed to be expressed to produce the enzymes
  • If one of the genes is not expressed, intermediate precursor will not be produced (e.g. that color will not be expressed)
  • This also means that all the consecutive precursor molecules cannot be formed & the final product cannot be formed as this is an enzyme cascade
  • Effectively all the consecutive genes were masked by the lack of expression of a previous gene in the pathway

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