system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is it decided which gene is dominant and which is recessive? Does each gene have some sort of "score" and the highest one between a pair is expressed?
gpt
Let's say a gene is responsible for making a certain protein. The gene has two alleles - one that makes the protein and one that doesnt. Producing the protein causes a certain trait to be expressed. This makes the trait dominant - if you have one copy of the allele that can produce the protein, then you will have the trait.

On the other hand, let's say there's a trait that is expressed only if you don't have that specific protein. This means that the trait is recessive, because you need both alleles that can't produce the protein in order to have it.