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molecular revolution
The first molecular markers: allozymes
AllozymesEnzymes 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)
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
+
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Substrate enzyme Visible
Product
Lab assay of isozymes
Isozyme gels
Quaternary Structure and Allozymes
• Enzymes can consist of several subunits• Monomer
• One subunit
GenotypeAA AB BB
– Dimer• Two subunits
– Tetramer • Four subunits
Disparate viewpoints about true levels of genetic variation
• classical+ + + m + ... + + +==============+ + + + + ... + + +
• balancedA1 B2 C3... X1 Y1 Z3=================A4 B2 C7... X1 Y1 Z2
Allozymes revealed unexpectedly high levels of genetic variation
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?