Q1. Activation of T cells requires that antigens be presented from antigen-presenting cells, not simply by exposure to the antigen in solution. What biological rationale may underlie this requirement - consider both from the perspective of how this can aid in the generation of a cytotoxic T cell response, and how it might aid in avoiding undesirable T cell responses.

Q2. What is the biochemical pathway that corresponds to duplicate dominant epistasis in genetics? There is a 15:1 ratio of phenotypes, there are two genes involved: A and B. but what is biochemical pathway that causes this ratio to form?