There are basically three types of research that can work for BS/MD programs. The first is the student’s own research often done for science fairs. This may be completely independent or a takeoff of some research done with a college professor. Either is fine. With this type of research you don’t need to win science fairs but it will strengthen your application if you do well as least at the state level. This is generally the most time intensive type of research.
The second type of research that is appropriate is research done under the guidance of a college professor. You will need to find a professor to do the research with and it will involve helping the professor with his or her research. This can be done during a single summer or during multiple summers or even on occasion multiple years.
When students talk about getting published it is usually this type of research that they are talking about. Getting published is something that college professors work on and they will sometimes include their lab assistants on the publication as additional authors.
This type of research gives the student a good level of research background but also has the additional benefit of providing some indication of maturity since it takes a fairly high level of maturity to ask a college professor if you can work with them in their lab.
The third option for research is at one of the research programs held by various colleges around the country every summer. These are generally what is known as pay for play because you just need to pay for the experience you receive. This type of research is less desirable than the first two options but if you haven’t been able to do anything in the first two categories these options are better than having no research experience at all. Some of these summer college programs provide a strong exposure to research while others are more oriented toward just talking about research and how it is done. The former is obviously to be preferred.
I have had students admitted to BS/MD programs and studies about Humanized Mice without research experience but you will be a much stronger candidate if you have one of these types of experience. If you get started early enough I generally recommend one of the first two types of research to strengthen your application.