Writing sample requirement for PhD application - submit something you assisted in writing? I'm applying to PhD programs and some require writing samples with a reminder of prioritizing works that are related to the phd program or to my research proposal. The only related writing I have is the paper I'm working on now as a research assistant.
The research topic is my professor's of course, and I'm sure I will not be listed as a co-author. I did write the paper from scratch, but the professor has constantly reviewed its structure and content, and provided comments on things that need to be changed. I did the literature review (research, reading, synthesis, writing), the data collection, statistical analysis, and discussion of results.
I would say that for the current version of the paper, content is 80% mine. Of course, the seed idea was the professor's, but the concept of the paper has changed based on my input after I did the literature review. Would it be okay to submit a portion of this as a writing sample for my phd applications? Or is this not allowed since I'm just a research assistant and not a co-author? Also, the paper is meant to be submitted to a journal for publication so will it be illegal for me to submit a portion of it as a writing sample? I will definitely not send the results sections.
Thanks!
Would it be okay to submit a portion of this as a writing sample for my phd applications?

Yes. (Personally, I'd submit the whole paper.)

Or is this not allowed since I'm just a research assistant and not a
co-author?

You should make the circumstances clear, e.g., the seed idea was the professor's, the literature review is yours, your literature review influenced the concept of the paper, you wrote 80% of the material, and anything else that's relevant.

Also, the paper is meant to be submitted to a journal for publication so will it be illegal for me to submit a portion of it as a writing sample?

Sharing preprints is fine.

I will definitely not send the results sections.

You can send the results section. If there's concern over IP theft, just make the entire paper available as a technical report.