One exceptional serum was discovered. 

 This serum appeared to have antibodies that 

 were relatively more amenable to fraction- 

 ation. Absorption of this serum with the 

 cells of a Bristol Bay fish left consider- 

 able antibody for the cells of a Columbia 

 River fish while absorption with the cells 

 of the Columbia River fish removed all the 

 antibody for both types. The small amount 

 of this serum that was available prevented 

 a systematic expansion of this observation. 

 However, the occurrence of this serum shows 

 that a study of the serums of other pigs 

 may prove to be profitable. 



The discovery that the erythrocytes 

 of salmon from different geographic areas 

 vary significantly with respect to their 

 reactions with antibodies in pig serum 

 raises the question of the nature of the 

 mechanism controlling this variation. 

 While the answer to this question awaits 

 further study, several sources of evidence 

 indicate that a genetic mechanism probably 

 exists. First, the erythrocyte antigens 

 of mammals and birds have been found to be 

 genetically determined wherever investi- 

 gated. Second, Hildeman (1956) has shown 

 that certain erythrocyte antigens of gold- 

 fish have hereditary determinants. Third, 

 different species of salmon, (Ridgway and 

 KLontz, 1957) as well as other species of 

 fish, (Suyehiro, 19^-9 > Cushing and Sprague, 

 1953); show characteristic species speci- 

 ficities with respect to their erythrocyte 

 antigens. This suggests that the antigenic 

 specificities involved are genetically 

 determined. 



An analysis of the frequency distri- 

 butions of the antigenic variations in 

 sockeye salmon populations was made with 

 the Hardy-Weinberg formula (Srb and Owen, 

 1953) in an attempt to obtain further 

 information concerning the possible ge- 

 netic background for these variations. 

 The Hardy-Weinberg formula relates the 

 frequencies of allelic genotypes to the 

 frequencies of allelic genes in a randomly 

 mating population, in terms of the binomial 

 expansion. It was through the use of this 

 formula that Bernstein determined the 

 exact method of inheritance of the human 

 ABO groups (see Race and Sanger, 1954) and 

 it is an indispensable tool in the study of 

 the population genetics of blood groups in 

 man and animals. 



Our interpretation of the data pre- 



sented is based upon the, assumption that 

 the observed variations in strength of 

 agglutination, expressed in terms of high, 

 intermediate and low scores, are due to 

 two primary causes. 



The first is that the active aggluti- 

 nin in serum WP4 has a lower affinity for 

 a qualitatively different but related anti- 

 gen on the surface of the lower scoring 

 cells than for the antigen on the higher 

 scoring cells. Since our absorption re- 

 sults indicate that these antigens must be 

 serologically related, because they react 

 with the same agglutinin, we assume that 

 they are determined by allelic genes. 

 Differences in the strength of agglutination 

 brought about by the reaction of one type 

 of antibody with different antigens de- 

 termined by allelic genes are well document- 

 ed in the literature on blood groups (Race 

 and Sanger, 1954). 



The second primary cause of variation 

 must be postulated to account for the inter- 

 mediate reactions. This is assumed to be 

 a dosage effect causing a stronger reaction 

 with cells of individuals homozygous for a 

 particular gene than those of individuals 

 heterozygous for this gene. Dosage effects 

 exhibited by blood grouping reagents are 

 also well documented in the literature; in 

 fact, the scoring system used by Race, 

 Sanger and Lehane (1953) in their study of 

 the dosage effect in the human Duffy blood 

 groups serves as a model for our scoring 

 system. 



The apparent trimodality of the 

 distribution of agglutination scores 

 (Figure 1) served as a basis for assigning 

 individual fish to one of three categories, 

 rated as strong, intermediate and weak 

 reactors. These categories, as explained 

 above, may be postulated to correspond to 

 three genotypes determined by a single 

 gene and its allelic alternates. Strong 

 reactors are considered as homozygous for 

 this gene (symbolized AA), intermediate 

 reactors as heterozygous (Aa) and weak 

 reactors as lacking this gene (aa). The 

 numbers of fish occurring in each category 

 are compared with those expected on the 

 basis of the Hardy-Weinberg formula in 

 Table 3. 



Two groups of fish drawn from spawn- 

 ing populations were also studied. These 

 were taken from the Okanogan River and the 



