Shell color in crabs is determined by a polygenic inheritance system, possibly involving involving as many as 9 genes. For simplicity let’s consider the influence of 3 genes: A, B and C, where a dominant allele darkens shell color .


Crab A: aaAAaaABaABC

Crab D: aaaaAAaaBaaa

Crab B: aaAAaaBaCaaa

Crab C:aaAAaaaaaaaa