Figure 1.

Barriers to gene flow detected in Atlantic herring and European flounder, along with the geographical distribution of frequencies of two alleles at the heat-shock protein gene Hsc70 in the flounder. The map shows the main barriers (that is, zones of lowered gene flow) detected by analysis of microsatellite DNA markers in Atlantic herring [18,19] (red dotted lines) and European flounder [21,27] (blue dotted lines). The pie charts denote the frequencies of two alleles (indicated by black and white, respectively) at the Hsc70 locus in the European flounder at the indicated locations [27].