Which one is not a molecular marker?
Molecular markers are defined as detectable DNA sequence variations that reveal polymorphism at the molecular level, including RFLP, RAPD, AFLP, SSR, SNP and similar techniques based directly on genome variation. Isozymes are multiple forms of enzymes differing in amino acid composition, charge and electrophoretic mobility, detected through biochemical staining after native gel electrophoresis. They reflect gene product variation rather than direct DNA polymorphism, influenced by post-translational modifications and tissue-specific expression. Though historically used, they are classified as biochemical markers, not DNA-based molecular markers.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.