<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>Under the microscope chromosomes appear as thin, thread-like structures. They all have a short arm and long arm separated by a primary constriction called the centromere. The short arm is designated as p and the long arm as q.</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>