GRANT ET AL.: POPULATION GENETICS OF YELLOWFIN SOLE 



Twenty-one invariant bands appeared on the gels 

 and each was interpreted to reflect the gene products 

 of a monomorphic locus. Although these loci pro- 

 vided no information about differences among popu- 

 lations, they were routinely scored to provide a basis 

 for computing average heterozygosities and genetic 

 distance, both of which require a large sample of ran- 

 domly selected loci. The following proteins were con- 

 trolled by one or more polymorphic loci. 



Adenosine Deaminase (Ada) 



Two loci with different tissue expressions were 

 observed. The last anodal locus, Ada-2, had a num- 

 ber of single- and double- banded phenotypes which 

 reflected homozygotes and heterozygotes of seven 

 alleles (Fig. 2). Double-banded heterozygotes sug- 

 gest that the subunit structure of this enzyme is mono- 

 meric. Similar phenotypes have been observed in 

 Pacific herring (Grant 1981) and in North Atlantic 

 pliace, Pleuronectes platessa (Ward and Beardmore 

 1977). 



Glucosephosphate Isomerase (Gpi) 



The most common phenotype of Gpi had three 

 bands reflecting the gene products of two loci where 

 the central band represented the heterodimeric pro- 

 duct between the two loci (Fig. 2). Several single- and 

 triple-banded phenotypes were observed at each 

 locus along with corresponding interlocus hetero- 

 dimeric bands. 



Isocitrate Dehydrogenase (Idh) 



Two zones of activity having different tissue dis- 

 tributions appeared to reflect the products of two loci 

 where heterodimeric bands between the loci did not 

 form (Fig. 2). The more anodic oocus, Idh-2, was 

 expressed predominantly in liver was invariant. Idh-2 

 had a number of single- and triple-banded pheno- 

 types reflecting the products of four alleles. 



Malate Dehydrogenase (Mdh) 



The following genetic model of Mdh is based on the 

 observation of several low-frequency variants (Fig. 

 2). The most common phenotype consisted of four 

 bands, the least anodic of which is designated as the 

 homodimeric band of Mdh-1. The products of this 

 locus do not form heterodimeric bands with the pro- 

 ducts of other Mdh loci. An analogous locus appears 

 in salmonids (May et aL 1979) and in Pacific herring 

 (Grant 1981) and is considered to be mitochondrial 



The next anodic band of the common phenotype 

 reflects the products of a single locus, Mdh-2, having 

 single- and triple- banded variants. The third band of 

 che common phenotype represents a heterodimeric 

 band between Mdh-2 and Mdh-3. At Mdh-3 there 

 were triple- and broad- banded heterozygotes with 

 corresponding heterodimeric bands with Mdh-2. 



Mannosephosphate Isomerase (Mpi) 



One zone with rare two-banded heterozygotes was 

 observed for this monomeric enzyme. 



Peptidase (Pep) 



Three polypeptide substrates were used to detect 

 the products of five peptidase loci. Pep-2 was 

 segregating for five alleles that produced single- 

 banded homozygotes and triple-banded hetero- 

 zygotes (Fig. 2). The remaining peptidase loci ap- 

 peared to be monomorphic. 



Phosphoglucomutase (Pgm) 



There appeared to be two loci with different tissue 

 expressions. The locus, which was predominantly 

 expressed in skeletal muscle tissue, had several dif- 

 ferent single- and double-banded phenotypes 

 reflecting the products of seven alleles (Fig. 2). Pgm- 

 2, which was best visualized with extracts of heart 

 and liver tissues, was monomorphic. 



Phosphogluconate Dehydrogenase (Pgd) 



The products of Pgd were interpreted to be coded 

 by a single locus having five alleles. Heterozygotes 

 were triple- or broad- banded depending upon the 

 relative mobilities of the variant alleles (Fig. 2). 



Population Structure 



The proportion of polymorphic loci was similar to 

 that observed for other teleosts. The frequency of the 

 most common allele was 0.99 orlessfor 10 loci(329c), 

 including 4 loci — Ada-2, Gpi-1, Gpi-2, and Pgd — 

 which were polymorphic at the 0.95 frequency 

 criterion. The allelic frequencies of these 10 

 polymorphic loci are presented in Table 4. A complete 

 set of data was not available for samples collected 

 between 1975 and 1978, so these data were only used 

 to test for differences between these samples and 

 those collected in the same areas in the eastern Ber- 

 ing Sea in 1979 and 1980. The remaining statistical 

 analyses were applied only to data collected in 1979, 



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