Interpretation of Isozyme Banding Patterns in Haploids

For haploid fungi, each individual ideally will produce a single band on a gel. Such isozymes can be scored easily by assuming that each band corresponds to an allele at a single genetic locus. Each allele can be named by indicating its relative migration distance on the gel. The easiest approach is to designate the most common allele as number 100. Then all other alleles can be indicated by their migration distance relative to the 100 allele. For example, an allele migrating 14% faster than allele 100 would be allele 114, and one migrating 13% slower would be allele 87 (Figure 1).

More than one band per haploid individual may indicate multiple loci. If alleles at each locus migrate within a limited, defined region of the gel then it may be possible to score each locus separately. Alleles at each locus can be named as indicated previously but with a locus designation, e.g., Gpi-1 100 and Gpi-2 100 to indicate the 100 alleles at two loci coding for the enzyme glucose-6-phosphate isomerase. Enzymes giving more complicated banding patterns in haploids should be avoided as accurate interpretation is almost impossible without thorough genetic analysis. "Null" alleles—those in which no enzyme activity is detected— should be regarded with suspicion as it is difficult to distinguish a null allele from a null caused by faulty technique. Furthermore, it is difficult to imagine a haploid being truly null for important enzyme activities. All potential null alleles should be verified thoroughly—most probably will turn out to be errors caused by poor enzyme extraction from particular individuals or other problems with technique.

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