Identical twins share the same genetic makeup (DNA) because they are formed from a single zygote (fertilised egg). However, fingerprints are not an entirely genetic characteristic. They are determined by the interaction of genes in the developmental environment of the womb.
Fingerprints are created in about the 13th to the 19th week of foetal development. There are a variety of factors which influence the fingerprint patterns, such as the length of the umbilical cord, the blood pressure, position of foetus in the womb and rate of finger growth at the end of the first trimester.