Table 2 Similarities and differences between bacterial and eukaryotic genome-wide association study approaches

Ploidy

Haploid

Diploid

Genetic re-assortment

Infrequent short gene conversion and horizontal gene transfer events

Homologous recombination and chromosome segregation linked to reproduction

Accessory (non-core) genes

Variable numbers in different species

Rare

Linkage disequilibrium

Variable across the genome and between species

Variable across the genome

Population structure

Asexual, generally highly structured, except for relatively rare homologous recombination events

Sexual, variable allele frequencies in subpopulations owing to non-random mating, ancestral divergence, drift

Confounders in genome-wide association studies

Population structure

Population structure

How to move from association to causality

Genetic reconstruction of mutations in laboratory strains, transposon mutant screens

Forward genetics in animal models or cultured tissue systems; linkage to known genetic diseases; large monogenic association studies

Current burden of proof for causality

Molecular Koch’s Postulates

Combined genetic and experimental evidence