A level Biology exam revision resources written by A level Examiners





 

Epistasis is an unusual case of dihybrid inheritance. It involves two separate genes that together determine one characteristic. This can occur when the genes code for enzymes which are involved in the same metabolic pathway. An example of this in the flowering sweet pea plant is shown below, in figure 1.

Figure 1
Epistasis

Separate genes code for the two enzymes and their alleles are shown in table 3, below.

Table 3
Epistasis

Both enzymes A and B must be present for purple flowers to be produced. A genetic cross involving these genes is shown in the diagram below.

Epistasis
Epistasis


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