Heterozygosity-fitness correlations: new perspectives on old problems.

Heterozygosity-fitness correlations (HFC) have been studied in various organisms for more than two decades, but they are not universal. Although their detectability is limited by several factors (null alleles, inaccuracy of the phenotypic description of fitness, small sample sizes) the correlations appear intrinsically weak and often inconsistent across samples. Determining the origins of HFC is therefore a complex task. However, this issue might soon be resolved provided clear hypotheses and definitions are used (especially, if the problem of the neutrality of allozyme variation is not identified with the related issue of HFC), as well as new empirical (molecular markers) & theoretical (statistical models) tools.