UTTER ET AL,: GENETIC POPULATION STRUCTURE OF CHINOOK SALMON 



APPENDIX B 



Previously Unreported Genetic Variants 



Glutathione reductase (Gr) was the more readily 

 interpreted of the two previously undescribed poly- 

 morphic enzymes observed for chinook salmon in 

 this study. The phenotypic forms (App. Fig. 1) were 

 those expected from a dimeric enzyme with three 

 alleles and were consistent with known allelic 

 variants of Gr observed in other vertebrates (e.g., 

 man) (Harris and Hopkinson 1976). The assumption 

 that this variation was a three-allele polymorphism 

 was supported by the conformance of phenotypic 

 ratios to those expected under Hardy-Weinberg 

 equilibrium, the absolute repeatability of expression 

 from independent extractions, and the parallel 

 expression of different tissues (eye and skeletal mus- 

 cle) from individuals expressing a given phenotype. 

 The previously undescribed glucose-6-phosphate 

 isomerase (Gpi) variation was less readily explained. 

 Individuals homozygous for the common alleles at 

 each of the three Gpi loci express a six-banded 

 phenotype that is directly interpreted as having 

 three homodimeric and three heterodimeric bands 

 (App. Fig. 2). An extension of this interpretation 

 also explains additional numbers of bands which 

 arise from allelic forms having different mobilities, 

 or fewer bands resulting from either allelic forms 

 of different loci having common mobilities or from 

 null alleles. However, none of these explanations 

 adequately describe the five-banded Gpi phenotypes 



that have been found with regularity in some 

 collections. 



One explanation that is consistent with the ob- 

 served phenotypes is that the subunits encoded by 

 a locus aggregate randomly, but that the aggrega- 

 tions for some interlocus combinations are pre- 

 cluded. Such inhibited combinations are common 

 among duplicated loci of salmonids. For instance, 

 subunits of Ldh-3 and Ldh-5 randomly aggregate, 

 as do those of Ldh-3 and Ldh-4; however, Ldh-4 and 

 Ldh-5 subunits do not aggregate (Wright et al. 

 1975). Mutations precluding aggregation (but not 

 necessarily affecting electrophoretic mobility) must 

 have arisen at some time between the duplication 

 event and the present, and such mutations must 

 have been polymorphic between their arising and 

 their fixation (see Allendorf and Thorgaard 1984, 

 for a review of gene duplication in salmonids). 



The above model was tested when gametes and 

 tissues were obtained from individuals of the Priest 

 Rapids stock where five-banded Gpi phenotypes 

 were commonly observed. Because of difficulty in 

 unambiguously discerning common and presumed 

 heterozygous phenotypes, the only informative 

 crosses were those involving the single parent hav- 

 ing a five-banded phenotype. The phenotypic ratios 

 of the two matings involving this individual (App. 

 Table 1) conform to those expected from a Men- 



^«, 



Sample 

 number 



1 23456789 



10 11 12 13 14 15 16 17 18 19 



Appendix Figure 1.— Glutathione reductase phenotypes of chinook salmon from eye fluid extracts. Genotypes in- 

 clude 100/100 (samples 1, 2, 4, 9, 10. 15, 18, 19). 100/85 (samples 3, 6, 14, 16), 85/85 (samples 5, 17), 85/110 (sample 

 7), 110/100 (samples 8. 11, 13), 110/110 (sample 12). 



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