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    the OCR textbook explains how epistasis can work in a complementary fashion and produce purple flowers even if the parents are white. But I don't understand this diagram.

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    The book says that 'at least one dominant allele for both gene loci (C-R-) has to be present for flowers to be purple'. If that's the case then why does the diagram have C/c and R/r and not just C and R? :confused:

    It doesn't say just C and R because it is possible for each gene to be Rr or Cc and they would still be expressed as the purple colour. Both alleles don't have to be dominant for the purple colour to be expressed. The diagram shows that unless you have a dominant C and R the flowers will be colourless/white, due to the genes masking the purple colour. So the R and C genes at different loci have to work together to produce the purple colour...hope this helps
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