Download Isozymes

molecular revolution
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)
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Allozyme assay
• Gel electrophoresis
• Current
• Charge
• Gel matrix
• Starch or other medium
• Protein variation
• Charge
• depends on pH
Substrate
• Size
• different length of AA chain
• Shape
• Tertiary and quaternary structure
• Visualization
• Uses enzyme reactions
• Specific substrate for each allozyme
enzyme
Visible
Product
Lab assay of isozymes
Isozyme gels
Quaternary Structure and Allozymes
• Enzymes can consist of several
subunits
• Monomer
• One subunit
– Dimer
• Two subunits
– Tetramer
• Four subunits
AA
Genotype
AB
BB
Disparate viewpoints about true levels of
genetic variation
• classical
+ + + m + ... + + +
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+ + + + + ... + + +
• balanced
A1 B2 C3... X1 Y1 Z3
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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?