An investigation of the evolution of populations under the influence of a rough 'fitness landscape' in which interactions between genetic loci play an essential role is conducted. Background in population genetics is presented and the history of thought on the reason for sexual reproduction is reviewed. The impact of sex due to recombination is analyzed in the case of the minimal frustrated fitness landscape. Modular polyketide synthases, an interesting biological system with medical relevance, are investigated. The effect of recombination on the search for novelty is proposed as the cause of 'collinearity' in these systems, an observed strong correlation between genetic order and functional order. Finally, correlations between genetic changes in Drosophila coding sequence are considered. These correlations are quantified from sequence data and the results presented. A strong signal of clustering of non-synonymous changes is found in both divergence and polymorphisms. It is proposed that compensatory interactions between nearby amino acids best explains the observed clustering.