According to the documentation for the Multiple Choice question type ↗:
"With multiple-answer Multiple Choice questions, each answer (choice) may carry a positive or negative grade. If the total grade is negative then the mark for this question will be zero."
"With single-answer Multiple Choice questions, you can specify negative or non-negative grades for each answer. A single-answer Multiple Choice question can result in a negative mark if its behaviour is set to Deferred feedback, but not other modes (Adaptive mode, Interactive with multiple tries, etc.)..."
If you have more than one question in a quiz, the total mark is the algebraic sum of the marks for each question. So if you have a negative mark for a "single-answer Multiple Choice question in a quiz with Deferrred Fedback behaviour", this negative mark will be subtracted from the marks for the other questions. However, if the total mark for the quiz is negative, the grade in the gradebook will be zero.
There might be other question types that accept negative marks, but I don't know about them. Also, I don't think there can ever be any negative grades in the gradebook.