Many twins or parents to twins are often asked if they are identical. Sometimes the answer is easy, but not always. Identical twins will often have more similar behaviour then fraternity twins. As we grow older it may be important to know if a twin-person is identical with another twin-person or not.

Although identical twins often look so much alike that we have difficulty recognizing one from the other, not all identical twins are mirror images of each other.
Although identical twins have the same genotype (identical DNA), different expression of paternal or maternal genes on chromosomes lead to different phenotypes.

Traits such as fingerprints and physical appearances in twins are a result of an interaction between their maternal and paternal genes and their expression in the uterus. Some twins may be mirror images of each other and therefore do not look identical and in fact identical twins can have different hair colour.