The q arm is the longer segment of a chromosome extending from the centromere. It follows the p arm in naming, simply as the next letter in the alphabet. Like the p arm, the q arm contains genes essential for cellular function, though it often holds a larger number due to its greater length. Gene mapping commonly uses q arm locations, such as 7q or 17q, to identify specific genetic regions. The q arm works together with the p arm to form the full structure of the chromosome. Its size and gene content vary widely across different chromosomes.