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happens to predominate in Etter Pond and is found in very low frequency in other razorback populations (Figure 1). If Ck-A was the only locus to suggest hybridization, we would be concerned about this alternate explanation. However, "flannelmouth" alleles at Ada-A2, mIcdh-A, and mMdh-A1 were also identified (albeit at low frequency) in the Etter Pond sample raising coincidence beyond reasonable expectations. The assymmetry of introgression at the marker loci is especially interesting, but explanations (e.g. selective differences) would be speculative at this time. Status of Etter Pond razorbacks.- The razorbacks inhabiting Etter Pond represent at least a second generation beyond an original hybridization event. Tom Dowling (pers. comm.) examined these same 13 original razorbacks from Etter Pond and found only "razorback mitochondrial DNA (mtDNA)." Because of the maternal inheritance of mtDNA, one can conclude that the original hybridization involved female razorback(s) and male flannelmouth(s). A subsequent backcross of F1 x flannelmouth should have yielded more flannelmouth alleles at Ada-A2, mIcdh-A, and mMdh-Al than found (Table 1). A subsequent backcross of F1 x razorback should have produced many individuals homozygous for the razorback Ck-A allele (not found; Table 1). The most parsimonious explanation of the data in Table 1 would be that these specimens are the result of F2 x F2 pairings in which the creatine kinase expression of the parents was always RF (heterozygous) x FF ("flannelmouth" homozygote), which would yield only RF and FF offspring in equal numbers (exactly what is found in Table 1: 27 RF and 28 FF). These almost-equal numbers of Ck-A RF and FF are compatible with the result of a cross of a single F2 male and a single F2 female (or relatively few individuals among which one sex was all RF and the other all FF). We would have to speculate that a few more than two parents contributed to the current generation and that heterozygous conditions existed in perhaps only a single parent per diagnostic locus to explain the residual heterozygosity at the other diagnostic loci. In any case, the entire Etter Pond population is introgressed with alleles from hybridization with flannelmouth suckers. We strongly recommend that all Etter Pond specimens, and hatchery progeny, be destroyed to prevent the perpetuation and enhancement of genomic pollution of the greater razorback population. Other Colorado sources of razorback breeding stock.- Although based on only four specimens, the Highline Lake population exhibits no evidence of hybridization (Table 2). We raise the question of the exact origin of the three 1993 "Colorado River" specimens. If they indeed came from the Colorado River proper, then this population is also introgressed and should not be tapped for breeding stock. If, on the other hand, these specimens came from impoundments near the river and not the river proper (as in 1991; specimen RSB-008 Table 2), it may be that the impoundments are conducive to interbreeding and that the Colorado River population is not introgressed (even so, such a conclusion is based on only three 1988 specimens). 3