STATISTICAL GENETIC CONSIDERATIONS FOR MAINTAINING GERM PLASM COLLECTIONS

One objective of the regeneration of genetic populations is to maintai n at least one copy of each allele present in the original population. Genetic diversity within populations depends on the number and freque ncy of alleles across all loci. The objectives of this study on outbre eding crops are: (1) to use probability models to determine optimal sa mple sizes for the regeneration for a number of alleles at independent loci; and (2) to examine theoretical considerations in choosing core subsets of a collection. If we assume that k-1 alleles occur at an ide ntical low frequency of p0 and that the k(th) allele occurs at a frequ ency of 1-[(k-1) p0], for loci with two, three, or four alleles, each with a p0 of 0.05, 89-110 additional individuals are required if at le ast one allele at each of 10 loci is to be retained with a 90% probabi lity; if 100 loci are involved, 134-155 individuals are required. For two, three, or four alleles, when po is 0.03 at each of 10 loci, the s ample size required to include at least one of the alleles from each c lass in each locus is 150-186 individuals; if 100 loci are involved, 7 5 additional individuals are required. Sample sizes of 160-210 plants are required to capture alleles at frequencies of 0.05 or higher in ea ch of 150 loci, with a 90-95% probability. For rare alleles widespread throughout the collection, most alleles with frequencies of 0.03 and 0.05 per locus will be included in a core subset of 25-100 accessions.