Why Some Identical Twins Are Noticeably Different

I've always wondered why my set of identical twins sometimes aren't so much. One is left-handed and one is right.

This explains in some measure why identical twins -- products of nearly identical genomes -- can be noticeably different from one another in their appearance and propensity for disease. Living things are, after all, built from cells, and each cell is in turn the product of the genes it expresses. Dynamic and random allelic expression can result in different blends of some traits, even in otherwise genetically identical people.