Nelson et al.: Population structure of Oncorhynchus tshawytscha of the Fraser River 
105 
gence among populations with single 
locus values of 0.011 (SD=0.002) for 
Ots 101, 0.021(SD=0.QQ4) for OtslOO 
and 0.038 (SD=0.007) for Otsl02. 
The multiple locus value was 0.023 
(SD=0.008). To determine the pat- 
terns of genetic relationship between 
sample groups within the individual 
regional groupings, pairwise F st 
values were calculated for each pair 
of samples (Table 4). The highest 
pairwise F st values were observed 
between populations of different 
regional groups. In order to esti- 
mate the degree of genetic isolation 
between the regional groupings sug- 
gested by dendrogram analysis, popu- 
lations were combined by geographic 
region and pairwise F sl values were 
calculated (Table 5). The greatest 
value observed was between the 
Thompson River and upper Fraser 
River regions (0.0161) and the lowest 
value was between the upper and 
middle Fraser regions (0.006). F st 
values were significant at each locus: 
Ofs 101 0.006 (SD=0.002), OfslOO 
0.008 (SD=0.00)1, and Ofsl02 0.022 
(SD=0.008), for combined loci 0.012 
(SD=0.005) (all P<0.005). 
Discussion 
Our results show significant genetic 
diversity within and between chi- 
nook salmon populations spawning 
in the tributaries of the Fraser River. 
The genetic relationship between the 
populations from the different trib- 
utaries suggest that there are four 
regional assemblages: upper Fraser 
River, middle Fraser River, lower 
Fraser River, and the Thompson 
River. These regional assemblages 
are concordant with the interpre- 
tation of the population structure 
seen by Teel et al. (2000) based on 
allozyme analysis. This concordance 
was observed with two very differ- 
ent marker sets. We employed three 
markers with average observed het- 
erozygosities of 86%, 88%, and 71%, 
whereas out of the 25 polymorphic 
enzymes used by Teel et al., the high- 
est heterozygosity was 0.441. The 
concordance of these two marker 
types with geography suggests that 
the genetic differences observed are 
not due simply to genetic drift but 
