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Table I. Hypothetical data on the genotypes of 10 individuals at three genetic loci: A, B and C. Dominant alleles are represented by capital letters and recessive alleles by lowercase letters. Locus C has a dominant allele, C, and four recessive alleles, c,, c., e3 and c4. Individual number Locus A Genotype at Locus B Locus C I AA BB Cc, 2 AA Bb c,c, 3 AA BB Cc, 4 AA Bb Cc3 5 AA Bb cicz 6 AA BB eIe3 7 AA BB Cc4 8 AA Bb eie4 9 AA BB cic3 10 AA bb c i cz Another aspect of genetic variation is allelic diversity or the number of different types of alleles at a locus. Empirical studies have shown that there is little or no variation at many loci, that is, most or all individuals in the population are homo- zygous for a single allele (as at locus A in our example) (Fuerst and Maruyama 1986). If other alleles occur at the locus, they are very rare. Other loci are highly polymorphic, that is, several alleles at the locus are reasonably common within the population. The concept of allelic diversity also is shown in Table 1. There is no allelic diversity at locus A, as only one allele, A, is present. There is some allelic diversity at locus B, with two alleles, B and b present. There is a great deal of allelic diversity at locus C, where there are five alleles present: the dominant allele C and four recessive alleles represented as c,, c2, c3 and c4. Although the data shown in Table 1 are hypothetical, actual data of this type, at least for some small fraction of the many genetic loci present in any species, can be obtained for most wild populations by collecting blood or tissue samples and using various descriptive genetic techniques, such as protein electrophoresis (Lewontin 1974). Pedigrees Versus Laboratory Data The goal of current strategies for maintaining genetic diversity in a captive pop- ulation is to preserve as much as possible of the genetic variation, in the form of heterozygosity and allelic diversity, that was present in the wild individuals used to found the population. Laboratory data on the extent of genetic variation present in the population are not required; we can manage to preserve genetic variation with no knowledge of how much genetic variation there is to preserve! Current techniques rely on models of the expected loss of heterozygosity predicted by population genetic theory in the absence of mutations and selection (Frankel and Soule 1981, Lacy et al. in preparation, Soule et al. 1986) and various analyses of the captive population's pedigree, including computer simulations of the loss of hypothetical alleles (Ballou in press, Hedrick and Miller 1992, Lacy 1990, MacCluer et al. 1986). Thus, although laboratory measures of genetic variation are not required, Managing Genetic Diversity ? 265