Lage et al.: Genetic structuring of Gadus morhua 



291 



44 



« 42° - 



40 - 



West longitude 



Figure 1 



Map of Northwest Atlantic sampling regions for Atlantic cod [Gadus morhua). 

 Dashed lines indicate the 100-m isobath. 



products were digested with the restriction endonuclease 

 Dral for at least 2 hours at 37°C and visualized on 2% 

 agarose gels to determine presence of Panl A or Panl B (or 

 both) allelic variants. 



Genetic analyses 



Samples were tested for conformation to Hardy- Weinberg 

 equilibrium (HWE) expectations by the Markov chain 

 method (Guo and Thomson, 1992) by resampling 2000 

 iterations per batch for 200 batches with GENEPOP 

 vers. 3. Id (CEFE/CNRS, Montpelier, France; available 

 at http://www.cefe.cnrs-mop.fr/) (Raymond and Rous- 

 set, 1995); the null hypothesis tested was random union 

 of gametes within a population. All loci were tested for 

 genotypic disequilibrium across the entire data set, as well 

 as for individual populations by using Markov chain resa- 

 mpling with 2000 iterations per batch for 200 batches in 

 GENEPOP vers. 3. Id; the null hypothesis tested was that 



the genotypes at one locus are independent from genotypes 

 at the other locus. 



Tests of allelic and genotypic differentiation among 

 and between population samples were conducted by using 

 FSTAT 2.9.1 (UNIL, Lausanne, Switzerland; available at 

 http://www.unil.ch/izea/softwares/fstat.html) (Goudet, 

 1995); the null hypothesis tested was homogeneous distri- 

 butions across samples. Because alleles can be considered 

 as independent when samples conform to HWE, it is valid 

 to permute alleles among samples to test for population 

 differentiation. On the other hand, when HWE is rejected 

 within samples, alleles within an individual cannot be 

 considered independent, and thus permuting genotypes 

 among samples is the only valid permutation scheme. In 

 both cases, contingency tables were generated and classi- 

 fied by using the log-likelihood statistic G (Goudet et al, 

 1996). Estimates of among- and between-sample F ST 's 

 were generated according to Weir and Cocherham (1984) 

 with FSTAT vers. 2.9.1 and GENETIX vers. 4.04 (available 



