Genetic architecture is the underlying genetic basis of a phenotypic trait and its variational properties. Phenotypic variation for quantitative traits is, at the most basic level, the result of the segregation of alleles at quantitative trait loci (QTL). Environmental factors and other external influences can also play a role in phenotypic variation. Genetic architecture is a broad term that can be described for any given individual based on information regarding gene and allele number, the distribution of allelic and mutational effects, and patterns of pleiotropy, dominance, and epistasis. There are several different experimental views of genetic architecture. Some researchers recognize that the interplay of various genetic mechanisms is incredibly complex, but believe that these mechanisms can be averaged and treated, more or less, like statistical noise. Other researchers claim that each and every gene interaction is significant and that it is necessary to measure and model these individual systemic influences on evolutionary genetics. Applications Genetic architecture can be studied and applied at many different levels. At the most basic, individual level, genetic architecture describes the genetic basis for differences between individuals, species, and populations. This can include, among other details, how many genes are involved in a specific phenotype and how gene interactions, such as epistasis, influence that phenotype. Line-cross analyses and QTL analyses can be used to study these differences. This is perhaps the most common way that genetic architecture is studied, and though it is useful for supplying pieces of information, it does not generally provide a complete picture of the genetic architecture as a whole. Genetic architecture can also be used to discuss the evolution of populations. Classical quantitative genetics models, such as that developed by R.A. Fisher, are based on analyses of phenotype in terms of the contributions from different genes and their interactions. Genetic architecture is sometimes studied using a genotype–phenotype map, which graphically depicts the relationship between the genotype and the phenotype. Genetic architecture is incredibly important for understanding evolutionary theory because it describes phenotypic variation in its underlying genetic terms, and thus it gives us clues about the evolutionary potential of these variations. Therefore, genetic architecture can help us to answer biological questions about speciation, the evolution of sex and recombination, the survival of small populations, inbreeding, understanding diseases, animal and plant breeding, and more. Evolvability Evolvability is literally defined as the ability to evolve. In terms of genetics, evolvability is the ability