A gene is best defined as: Select one: a. a nucleotide b. all of the DNA contained on a specific chromosome c. a nucleotide base pair d. a specific segment of DNA

The correct answer is d. a specific segment of DNA.<br /><br />A gene is a specific segment of DNA that contains the instructions for making a particular protein or performing a specific function in an organism. Genes are the basic units of heredity and are responsible for the transmission of traits from one generation to the next.<br /><br />Option a, a nucleotide, is incorrect because a nucleotide is the basic building block of DNA and RNA, but it is not a gene.<br /><br />Option b, all of the DNA contained on a specific chromosome, is incorrect because a chromosome contains many genes, and not all of the DNA on a chromosome is a gene.<br /><br />Option c, a nucleotide base pair, is incorrect because a nucleotide base pair refers to the pairing of two nucleotides (adenine-thymine or cytosine-guanine) in the DNA molecule, but it is not a gene.<br /><br />Therefore, the correct answer is d. a specific segment of DNA.