Manuel Navarulox asked:
Do identical twins have identical DNA? If so, do they have identical fingerprints? If they don't, how can this be because DNA is supposed to be the code which determines your make-up, hair colour, height and everything, so what's going on?
Identical twins do have identical DNA. They form when a fertilised egg, (that is when one sperm has joined with one egg to form a growing embryo) splits in two and it develops independently as two separate embryos. Because both halves originated from the same genetic material they are genetically identical. They are nature's clones and happen naturally in humans and some animals. In fact the nine-banded armadillo naturally produces four genetically identical offspring.
So twins are genetically identical but fingerprints differ amongst identical twins. The reason is that fingerprints are a developmental random process. When cells are migrating in the body, there are codes and chemical messages that tell them where to go in the body to put the body together, but when the cells get to their final destination, how they arrange themselves is much more random. Fingerprints are a consequence of this arrangement, so you will see a very individual picture to a personís fingerprints but of course their genetic fingerprint is going to be the same.
So your DNA doesn't tell you exactly how to build you! It's a bit like giving someone building instructions on how to build a wall, it doesn't tell you exactly where to put each of the bricks?