Final answer:
A gene is a (A) sequence of nucleotides in DNA that encodes the information for creating a functional RNA, which is then translated into a specific polypeptide chain. It is represented by three-letter codes that specify amino acids. Mutations in genes can lead to changes in the encoded proteins and phenotypes.
Step-by-step explanation:
A gene is best defined as A) a sequence of nucleotides that encodes a functional RNA. This sequence is found within DNA and consists of the instructions for making a specific polypeptide chain or RNA molecule. During transcription, a gene's sequence of nucleotides is used to create messenger RNA (mRNA), which then travels from the chromosomes to the ribosome, where it provides the template for protein synthesis. The genetic code within the gene corresponds to a series of three-letter codes that specify the amino acids to be linked together into a polypeptide chain. In cases where a protein has multiple polypeptide chains, each polypeptide is typically coded for by a different gene.
Mutations, such as loss of function or gain of function mutations, may alter the DNA sequence of a gene and consequently, the mRNA and protein produced, leading to changes in the phenotype of the organism.