Final answer:
A gene is a sequence of nucleotides that encodes the instructions for synthesizing a functional protein through the processes of transcription and translation.
Step-by-step explanation:
A gene is a sequence of nucleotides that encodes a functional protein. When a gene is expressed, the sequence of nucleotides in DNA is transcribed into messenger RNA (mRNA), which is then translated into a sequence of amino acids that form a protein. Each group of three nucleotides, known as a codon, corresponds to one amino acid in the protein sequence. This process is the foundation of how genetic information is used to produce the proteins necessary for cellular functions.