system
Given the following post, respond as if you're commenting on Reddit:
human
What makes a gene dominant or recessive?

What is the difference between a dominant or recessive gene? I know that dominant genes prevail over recessive ones and this is also the stuff I find on the internet. But I can't find an explanation of what makes a specific gene prevail over other ones in the fist place.
gpt
It depends on the details of what the gene does and how each allele (different version of the gene) works or doesn't work.

For example, lactose intolerance happens when _neither_ of your two genes for making lactase are functional in adulthood, so a single lactase-persistence allele will be dominant over a normal lactase-only-in-childhood allele. Or say you have a mutation in your ACE receptor that stops SARS-CoV-2 from binding: this COVID immunity allele would be _recessive_, because one copy of a normal ACE receptor would be enough to let the virus in. 

Then there are other situations, like making red pigments to color a flower petal, where having one allele just gives an intermediate phenotype (pink) compared to 0 (white) or 2 (red).