Final answer:
The best definition of a gene is that it is a region of DNA transcribed into RNA, encapsulating its role in heredity and protein synthesis.
Step-by-step explanation:
The most accurate definition of a gene currently is option C: A gene is a region of DNA that is transcribed into RNA. A gene is indeed a unit of genetic inheritance and plays a role in heredity, but to define it as the region that is transcribed into RNA is more precise. This definition encompasses the process of transcription, where a gene's DNA sequence is copied into messenger RNA (mRNA), which is then used in the process of translation to synthesize polypeptides, the building blocks of proteins. Not all genes code for proteins; some genes transcribe RNA molecules that have roles in regulation or other cellular functions.