general examples of "to code for"
Solution 1:
The answer would be in the scientific literature because this is a scientific usage. I assume that because the development of the genetic code occurred in the early 1960s and was partly carried out in the USA, the use of "code" as a verb and the somewhat colloquial expression "codes for" would have been more common than the (more proper) "encodes". Reviewers in the USA would generally not have a problem with "codes for" even in a formal scientific paper or a textbook. Nonetheless, to say that "Gene X encodes protein Y" is not only correct but preferable, in my view. This is because the information for protein Y is "contained within" the gene.