ISOZYME ALLELIC FREQUENCY CHANGES FOLLOWING MAIZE (ZEA-MAYS L) GERMPLASM REGENERATION

Germplasm collections serve the essential function of preserving genetic diversity. Genetic drift, the erratic, random fluctuation in gene frequency that can result from inadequate sampling during periodic regeneration of accessions, and selection have the potential to change the genetic identity of germplasm collections. Random genetic drift may lead to either fixation or loss of alleles. Small numbers of parents used in early regeneration cycles may reduce variability from that present in the original population. The degree of diversity in five maize germplasm accessions was measured as a function of isozyme polymorphism and allelic frequencies were examined following several cycles of regeneration. A statistical procedure was used to test whether observed allele-frequency variation from cycle to cycle of regeneration was consistent with a hypothesis of drift acting alone or if a linear trend indicated possible selection. The results indicated that most of the fluctuation observed in allelic frequencies can be attributed to random genetic drift. Alleles present in low frequencies were not represented in each cycle of regeneration as a result of sampling error.