Some of them we know a great deal about because we've been studying them for 25 years. But actually a shocking percentage of them we don't know anything about what they do. We just know they're there. Figuring out what the parts do will be one of the thrusts of the research at the Institute. One way to go about it is to make a mutation in the gene and then see what goes wrong when that gene isn't working.
Scientists then deduce what the function of that gene is.
For instance, in the mouse genome, which is her particular area of research, she studies a gene that if mutated completely deletes the gene. Nothing bad happens to the mouse. Now that is a conundrum because this gene is in all mammals. It is highly conserved. Evolution wants that gene there.