system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: at the molecular level what is the difference between a dominant gene and a recessive gene? What makes the dominant gene dominant and the recessive gene recessive?
gpt
It depends, but in a simple case if it takes multiple pieces to make the the final time e.g multiple protein "subunits" to make a "protein-complex" then if any of them are defective, the whole thing doesn't work.  Think of car tires where one or two of the four tires is flat (from the mutant gene) and the other two or three are fine.  The care is not going anywhere with flat tires, so having one good gene does not help.  Other genes/proteins work solo and if you have one bad copy the other good copy *might* be able to make up for it.  Just one example.

Another way is if you have half as much of the good protein is that enough?  If yes then the mutation is recessive, if not it is dominant.