1. molecular revolution

2. The first molecular markers: allozymes Allozymes Enzymes that diifer in amino acid sequence yet catalyze the same reaction -visible as a band on a gel -may exist at several gene loci Isozyme: allelic form of allozyme (same locus)

3. Allozyme assay Gel electrophoresis Current Charge Gel matrix Starch or other medium Protein variation Charge depends on pH Size different length of AA chain Shape Tertiary and quaternary structure Visualization Uses enzyme reactions Specific substrate for each allozyme + - Substrate enzyme Visible Product

4. Lab assay of isozymes

5. Isozyme gels

6. Quaternary Structure and Allozymes Enzymes can consist of several subunits Monomer One subunit Genotype AA AB BB –Dimer Two subunits –Tetramer Four subunits

7. Disparate viewpoints about true levels of genetic variation classical + + + m +... + + + ============== + + + + +... + + + balanced A1 B2 C3... X1 Y1 Z3 ================= A4 B2 C7... X1 Y1 Z2 Allozymes revealed unexpectedly high levels of genetic variation

8. Allozyme questions What type of DNA variation can you detect with isozymes? What is the ascertainment bias? Why were they wildly popular in the 1970’s and 1980’s, then disappeared by 2000?