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.
And yet when we take it away nothing happens. It could be that it so important that there's another gene that will compensate. It's a back-up. So that's why genetics isn't a perfect tool. Another tool is biochemistry, where scientists can purify the product of the gene and then try and understand what it's biochemical property is.