> > > > > Now assume you find a gene that seems highly conserved amongst a vast amount of species. But you have zero clue what it does. And you want to know. Usually, first step is to just delete it in a model and see what happens. Nothing happens? Okay, over express it. Nothing happens? Okay, try to see what the produced protein (theoretically or experimentally known) is similar to in sequence and structure (domains). That might give you a vague hint at what it might be involved it. If you have that hint, perhaps now you can delete it and challenge your cells or animal model with a stressor relevant to that hint. For example, perhaps you find the protein is similar to those involved in tight junctions, so now you can try to challenge your model with different deficiencies in whatever ions or other things to see if the mutated group is more severely affected.

Or you could screen for synthetic lethality / synthetic phenotypic alteration. It's not uncommon for there to be other genes that can compensate for the loss of your gene of interest; but then a double or triple mutant will usually have the relevant altered phenotype.