Background: Did an economics major after switching out of physics and I did a math minor in university with somewhat inconsistent math grades (A+, A-, D, C+, ... ). The reason behind my grade spread is, quite simply, a lack of consistent, deliberate, and persistent effort as an immature student. I am now very close to defending my MSc in resource and environmental economics with a 3.83 gpa in coursework, graduate awards, academic teaching & learning courses, conference proceedings, and hopefully a submitted paper for review by the time of my application , so there's been much growth for whatever that's worth.
Current Situation: I am trying to switch into mathematical biology to study similar natural resource problems I would in resource economics, but from a different perspective I find myself more drawn to. I have reached out to a potential advisor, they have my transcripts and CV, we are set for a video call to talk about me coming on as a PhD student.
Statement of Purpose: There are some math courses that I do not have as a result of not being a math major, and there are some courses I am planning to retake this academic year to boost the grades of the courses I did poorly in. In my statement of purpose, I am wondering how I can address the background gaps.
Initial Solution: After my chat with the potential advisor, I was thinking of writing out a concrete action plan (including MIT OpenCourseware, References to texts I would study from, and subject matter I would cover) to address the background gaps which would include a combination of taking courses and self-studying courses that are not being offered at my local institutions. This plan could then be submitted (appended?) to the Statement of Purpose.
The Final Problem: Given some deficiencies in background, how can one, or how should one, adequately address those deficiencies in a Statement of Purpose to communicate that by the time they enter the program, they would have a sufficient background to be successful in a program?
Many answers around Statement of Purpose tags have suggested that the statement be forward looking, and so I intend to not spend an inordinate amount of time talking about my history, and instead in the spirit of those answers, focus on the path forward.