Correlations and constraints

Genetic correlations between two phenotypic traits can impose constraints on evolutionary change. This correlation may be caused by pleiotropy (in which one genetic locus affects both traits) or by linkage disequilibrium (in which evolution maintains a non-random association between alleles at two distinct loci). In the November 28 Nature, Jeffrey Conner at Michigan State University, USA, describes correlations and constraints that influence the evolution of floral traits (Nature, 420:407-410, November 28, 2002).

Conner studied six traits in a natural population of wild radish, Raphanus raphanistrum, an obligate outcrosser. After nine generations of random mating (i.e. nine episodes of recombination), there were no significant changes in the genetic correlations between floral traits, implying that pleiotropy is the underlying genetic mechanism responsible for the correlations.