If I understand correctly, DNA determines which proteins are replicated within a cell, and therefore determine it’s function. So, it’s not as though DNA “knows” every cell in your body and builds out from a blueprint, rather your cells use DNA as instructions for how to respond to chemical stimuli.
This makes sense when talking on a small scale, like something in the environment triggering production of a specific enzyme. But what determines the creation and shape of complex organs or structures like eyes or fingers? What do those “instructions” look like? (“Keep building finger cells until blood circulation is low, then we have to start building fingernails”)?
In: Biology
The keyword you’re looking for is HOX genes (sometimes called homeobox genes). These are, broadly, a set of instructions that tell stem cells how to differentiate into different cell types, based on the cells surrounding them and the chemical signals they’re receiving. Mutations in HOX genes lead to deformities, including milder ones like extra fingers and toes, but also appendages growing where they absolutely should not be, or the absence of some structures entirely. For example, they can tweak certain genes in fruit flies to cause them to grow extra legs where their antennae would normally be.
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