Genes do not have a physical appearance because they are abstract units or regions of Deoxyribonucleic acid (DNA) or Ribonucleic acid (RNA) that code for a particular polypeptide or protein. DNA and RNA are molecules found in cells that carry genetic instructions. Think of genes as recipes that provide instructions for developing specific traits or producing certain substances within an organism. They consist of specific sequences of nucleotides (adenine, cytosine, guanine, and thymine in DNA; and adenine, cytosine, guanine, and uracil in RNA) arranged along the DNA or RNA strands. These nucleotide sequences encode the information needed to synthesize proteins or regulate cellular processes. Therefore, genes do not have a physical form or appearance; instead, they are defined by their functional role in carrying and expressing genetic information.