The p arm of a chromosome is the shorter segment extending from the centromere. The name “p” comes from the French word petit, meaning small. Despite its shorter length, the p arm can contain essential genes that contribute to normal cellular function and development. The exact gene content varies depending on the chromosome, meaning the p arm has no universal function across all chromosomes. Scientists use the p arm as part of a coordinate system to locate genes precisely, such as regions labeled 7p or 17p. Structurally, it plays a balanced role alongside the q arm in maintaining chromosome integrity.