Glycylalanine is a peptide formed by the linkage of two amino acids: glycine and alanine. This linkage occurs through a peptide bond, which is a covalent bond that joins the carboxyl group of one amino acid to the amine group of another with the release of a water molecule (a condensation reaction). Since glycylalanine consists of only two amino acids connected by a single peptide bond, it is classified as a dipeptide. Therefore, the correct answer is: