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So to me it seems like arms and legs are pretty similar that they almost have the same blueprint. And if you change part of it like the number of digits, you will have 12 fingers and 12 toes.

But at the same time there are differences.

So my question is, are arms and legs encoded with the same piece of DNA? Or two very similar pieces. But in that case why would a change in the arm blueprint to give you 12 fingers also give you 12 toes?

On the other hand if arms and legs are encoded by the same piece of DNA. How do legs develop heals and arms develop wrists?

Are arms and legs only different by their shape (morphology?).

Equally if a thumb is encoded by the same DNA as encodes fingers, (i.e. all are similar and have fingernails), why are thumbs different?

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    $\begingroup$ Welcome to Biology.SE. You might want to have a look at wikipedia HOX genes for a start. $\endgroup$ – Remi.b Mar 10 '17 at 1:04
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    $\begingroup$ I think that you might be interested in searching this: "Epigenetic mechanisms in fetal development" $\endgroup$ – Bob Mar 10 '17 at 1:18
  • $\begingroup$ it also helps if you don't think of DNA as a blueprint it is more like a recipe. there is no code for number of fingers there is a process that produces 5 fingers. you might want to do some background research on the wiki for limb development to get started. Then you should look up something called HOX genes. en.wikipedia.org/wiki/Limb_development $\endgroup$ – John Mar 10 '17 at 2:17
  • $\begingroup$ I think those other resources might be a bit too advanced. The simple way to consider genes is that they each have a thing that they do but that's only a tiny fraction (~2%) of our genome. Large amounts of the rest of the DNA controls /how/ those genes are expressed. So as our cells develop they go through a kind of dance. The DNA tells each cell how to prepare for the next move of the dance and depending on the cells environment (and other cells) the next moves of the dance can change. So many of the same genes used in making Arms are used for Legs, but it's a different way the cells dance. $\endgroup$ – Artem Mar 10 '17 at 6:03
  • $\begingroup$ So is the DNA a bit like this: [both][both][both][only-arm][both][both][only-arm][both][both][only-leg]. And the a protein(s) in the limb (arm) or (leg) tells which bit of DNA to activate? I guess that would make sense. I guess an [only-hand] bit of DNA could create a new protein (hand) and so on. Although maybe thats too complicated as hands and feet are very similar. $\endgroup$ – zooby Mar 10 '17 at 12:00

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