What if an undergraduate concentrated on research on the account of his study? I am studying medicine. We study different disciplines and different specialties during our undergraduate years.  My subject grades aren't very good. Then, I rushed to research and biostatistics -maybe to veil my low grades- and have made a little good progress at them while I am still undergraduate. Will doing this help me in my future? (I mean if I continued doing bad at the subject exams and concentrated on research methodology and biostatistics)
When you say you're studying medicine, I take it that you hope to be a doctor.

In which case it doesn't matter how brilliant you are as a researcher, if you can't acquire the necessary medical knowledge and clinical skills you'll never be competent or safe to practise medicine and your medical career will never get started. You may have a fantastic career as eg a medical statistician awaiting you. 

It's great if a doctor is research competent too, but being able to do research is not essential. Being able to examine, diagnose, and treat patients is.