The membranes of various organelles in the endomembrane exhibits variances in their lipid and protein compositions. These differences are largely established by the function of the Golgi apparatus in modifying, sorting, and directing membrane components to their final end point.
This is called incomplete dominance. When an something is heterozygous for an incomplete dominant gene, the resulting phenotype will be somewhere between the two. For example if a plant has a tall allele and a short one, but neither shows complete dominance over the other, the plant height will be somewhere in the middle.
