Medical Definition of Long arm of a chromosome
Long arm of a chromosome: The long arm of a chromosome is termed the q arm. All human chromosomes have 2 arms, the p (short) arm and the q (long) arm. They are separated from each other only by a primary constriction, the centromere, the point at which the chromosome is attached to the spindle during cell division. The symbol "p" stands for "petit", small in French, while "q" was chosen merely because it was the next letter in the alphabet.
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