FISHERY BULLETIN: VOL. 87, NO. 1 



phogluconate dehydrogenase (Pgd) and malate dehy- 

 drogenase (Mdh-2). In addition, three other loci— 

 aspartate aminotransferase (Aat), phosphoglucose 

 isomerase (Pgi), and xanthine dehydrogenase 

 (Xdh)— exhibited rare alleles (i.e., common allele (p) 

 > 0.950). SLx-phosphogluconate dehydrogenase pro- 

 duced a single zone of allozyme activity on the starch 

 gel that we interpreted as the product of a single 

 gene locus. The heterozygotes displayed three bands 

 which is typical of this molecule's dimeric structure 

 (Manwell and Baker 1970). In weakfish, Pgd ex- 

 hibited three alleles designated as 100, 98, and 96, 

 a rare allele. Both juveniles and adults had similar 

 frequencies of the most common allele (Table 2). 

 At the Mdh-2 locus, a dimeric protein product 

 formed heteropolymers with the products of other 

 Mdh loci. These heteropolymers occurred between 

 the products of Mdh-1 and Mdh-2, and Mdh-1 and 

 Mdh-3. The Mdh-2 locus was associated with liver, 

 and the Mdh-3 locus is thought to be expressed in 

 mitochondria (Thorne et al. 1963). This enzyme 

 system also displayed a fourth isozyme band that 



migrated cathodally. This Mdh isozyme band is not 

 reported in other similar studies and we do not know 

 what protein loci it represented (Fig. 2). The Mdh-2 

 locus was polymorphic and exhibited four alleles: 

 103, 100, 97 (a rare allele) and a fourth null allele 

 {Mdh-2 {N)). Two fish homozygous for Mdh-2 (N) 

 were found. One was in a sample of juvenile fish 

 from Spencer's Bay, NC and the other in an adult 

 from Chesapeake Bay. The frequencies for the most 

 common allele are found in Table 2. The uneven sam- 

 ple sizes (Table 2) occurred because of protein de- 

 naturation. The denatured samples indicated by 

 streaks in the gels were excluded from analysis. 

 Allelic frequencies of three samples differed sig- 

 nificantly from HWE for Mdh-2 (Table 2). This 

 deviation reflected a deficiency in the number of 

 heterozygotes which may have been due to the pres- 

 ence of the null allele (Selander 1970; Speiss 1977). 

 We estimated null allele frequencies from the square 

 root of the phenotype for Spencer's Bay (0.151) and 

 Chesapeake Bay (0.146). Using the mean of the two 

 values to estimate the null allele frequency for 



Table 2.— Allelic frequencies of juvenile and adult fish for Pgd and Mdh including 

 sample size, frequency of the most common allele and the standard error. All 

 samples were collected in 1982 unless otherwise noted. 



•HWE x^O.05 = 3.841, df = 1. 



••HW/E x^O.O! = 6.635. df = 1. 



•••HWE x^ 0,001 = 10.828, df = 1. 



'Geographic comparisons among regions of allelic frequencies for juveniles; x^ = 1 942, P 

 > 0.05, df = 2 (Pgd); x^ = 2 268, P > 05, df = 2 (Mdh) 



^Geograpfiic comparisons among regions of allelic frequencies for adults; x^ = 0.566, P > 

 0,05, df = 2 (Pgd), x' = 3 020, P > 0.05. df = 2 (Mdh). 

 'Represents a pooled sample, where samples <10 were combined. 



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