It's possible that a grad school would have an issue with this.
In my experience, admission to a graduate program is always contingent on successful completion of the undergraduate degree. The grad program will require a final undergraduate transcript and reserves the right to rescind admission if they're not satisfied with it. Presumably your application stated that you were working on a bioinformatics degree, and your admission was based on the assumption that you would complete it.
So it would be a good idea to contact the grad program and explain the situation. You probably don't want them to first learn about it when they get your transcript, and have them trying to guess what happened.
Some relevant questions:
What was the requirement in question? Is it some critical course that they might reasonably have expected every bioinformatics student to have?
Why didn't you complete it? Was a course not offered at a time when you could take it? Or did you fail a required course?
If (as your question seems to say) this was a new requirement, imposed after you started your degree, how recently was it imposed? Could you reasonably have fulfilled it?
What does your undergraduate advisor say about all this?