Lab internship recs

<p>I need two recommendations for a lab internship. I am already getting one from my PI, but I'm wondering who I should ask for my second one. My PI has taught me in class and is aware of both my academic and research performance. I could ask another professor but I don't need another person to talk about academic performance as I am applying to a lab, not grad school.</p>

<p>Is it ok to ask a TA? Will their rec still be taken seriously? I want to ask my TA who teaches my lab course. We learn techniques much different from what I normally do in my own research lab so if he spoke of those skills, I would seem more well-rounded in the lab. In addition, he has worked in the lab I am applying to. </p>

<p>It is generally far preferable to use a tenured or tenure-track professor for a letter of recommendation rather than a TA. Could the TA’s advisor co-sign the letter? Or is there anyone else who could write you a strong letter of recommendation - a professor whose class you went above and beyond in, or who you worked with in a non-class setting? (I have a letter of recommendation from a professor who I worked with mentoring a program for freshman STEM majors, for example.)</p>