Two Mice of the Same Species Have Different Ear Shapes

Two mice of the same species have different ear shapes.You find that one mouse, having normal shaped ears, was caught in a field in Kenya.The other mouse, with curled ears, was caught in the frozen tundra of Greenland.You determined that both mice have identical genotypes at the known gene loci controlling ear shape.How could you test the relative importance of environmental and genetic factors in determing ear shape?
This question as originally written is going to be confusing to some students because the question states that the two types of mice are identical at the genes that control ear shape so the answer appears obvious that the difference must be due to one or more environmental factors.Why would more testing be needed? I changed the wording of the question to "known gene loci" so that there may be genetic differences at other unknown loci and the answer would involve more analysis.To be consistent I made this change in question #129 also