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.