in terms of letters, most schools want at least two from science (Biology or Chemistry), and specifically, some schools require one Bio and one Chem. So right there, depending on where you are applying, you are lacking in the science/chem requirement. i agree with above comments, if you don't think its strong, don't use it. I would keep your genetics, physics, get a chem one if you can, and maybe a dentist you shadowed if you can. those four would be a solid mix. I used two biology, public health (but i knew it was a good one), dentist through aadsas, and then mailed my chemistry one straight to the specific schools that required it (I think Maryland needs it, if you're applying there...)