You Can Say That Again...You Can Say That Again

Q: Dear 100 Hour Board:

Why do "identical" twins have different finger prints?- Not so identical are they?

Irish Twin

A: Dear Celtic Brother,

Having an identical twin certainly does have its benefits: a free friend, an automatic transplant organ source, and a diabolical crime partner. Imagine you rob a bank, or knock-off somebody, and can blame it on your twin. The jury would never know who really committed the crime - and given just DNA evidence - either would Grissolm or the CSI team (no matter how much Prada they wear)! But if you left a fingerprint, it is true, the coppers could tell you apart from your twin. (Or if you have an identifiable tattoo that leads an eyewitness to correctly pick you apart).

Now, if you're being that nitty-gritty about it, identical twins don't exactly have the same DNA. They start out with the same zygoate (single fertilized egg) that splits: so on Day 1 they have the same genetics. But over time the environment inside the womb - and eventually outside - will change the DNA. Even naturally occurring mistakes in gene translation will cause differences. But things like different temperatures, blood flow, food, nutrients, position, etc in the womb can change the genes. Heck, DNA isn't even the same in all parts of your body. (Dr Starr, Stanford U)

Fingerprints are an amplified piece of this puzzle. The pattern of whorls, arches, loops are dermal ridges which are at first determined by genetic code in the baby. Around the 13th week of pregnancy the baby develops these, however immediately they are changed and influenced by the surroundings - ie. mother. Touching the amniotic sac, their face, what they eat, etc. changes the patterns slightly. But the changes are dramatically amplified in the patterns we see and therefore offer a distinguishing feature between twins.

Identical twins, similarly, aren't that identical when born. Their other features and genetics have the same influence of environment. This is all referred to as phenotype - the way we or species look. Genotype (DNA) + environment + random variables = Phenotype.

So yes. That extra helping of General Zhaos chicken when you are preggo could make your kid's fingerprints randomly closer to a mass murderer. You never know.

100 Hour Board

Oh and PS: Chance of having twins 1:40, identical twins 1:240, spontaneous fraternal twins 1:60, two sets of fraternal twins 1:5