Two letters of rec from the same lab- Does it look bad?

[ilovelab]

Will it look bad if I have two letters of rec from the same research lab? My boss is the head of the department and is barely in lab so we essentially have another PI for the wet lab. Would it look odd if both of them wrote letters of rec? I already have 2 other letters of rec from labs I did research in (genetics lab and ecology lab). I wonder if the letter of rec from the ecology PI wouldn't hold as much weight since its from a different discipline? 

[TakeruK]

Here is my opinion, but as I am not in your field, perhaps you would want to weigh the opinion of a biologist more highly. 

I don't think having two LORs from the same lab will "look bad" in the sense that it won't actively hurt you. However, it could potentially "waste" a LOR space that could have been used to highlight different positives about you. If the two LORs from the same lab will address different parts of your experience (sometimes your lab work can be neatly divided into two or more components, and each LOR can focus on each of these components). 

Since you do have another research PI LOR, I would suggest that you get a letter from the Ecology prof as your 3rd LOR instead of a second LOR from the same lab. This part might be field-dependent, but I don't think you need all three LORs to be from the exact same discipline. Many undergraduates have diverse research experience, because the point of undergraduate research experience is to try different things, not to specialize (that's what grad school is for).

However, if you didn't have a 3rd research LOR lined up and you were choosing between a second LOR from the same lab vs. a "did well in class" LOR, I'd say go with the second LOR from the same lab.