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?