One hypothesis that explains the result is : A) Two genes are involved with 12:3:1 epistasis, such that A_B_ and A_bb are black, aaB_ is brown,and aabb is green.

Explanation:

This is a case of Dominant Epistasis.
When two genes are involved and presence of dominant allele of one gene masks the effect of either allele of the second gene then the epistasis is termed as dominant epistasis.
In the given case black :brown: green ratio is approximately equal to 12:3:1.
Here presence of a dominant A allele that is responsible for the black colour masks the effect of either allele of B. Therefore A_B_ and A_bb produces black beetles
Again , absence of dominant A allows B to express itself and Brown beetles are produced thus aaB_ is brown.
When both the genes are present as recessive alleles, neither brown nor black colour is expressed and the beetles are green.Thus, aabb are green.

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3 years ago