Investigation of Genetic Factors Affecting Complex Traits Using External Apical Root Resorption as a Model

Genetic (genomic) and environmental (non-genetic) factors are the two main aspects that determine phenotype. Although there has long been a tendency to separate them (nature versus nurture), in essentially all traits (diseases) besides those secondary to trauma, both the genetic and environmental factors interact to develop the phenotype (nature and nurture). Traits (diseases) can be divided into two broad categories based on their genetic components pattern of transmission. The first category include so called simple (Mendelian) traits. The second category includes genetically complex traits. These are more common than Mendelian traits. They do not follow a clear pattern of inheritance, but they tend to run in families. Relatives of an affected individual or one who has the trait have an increased risk of developing the disease and or having the trait. The genetic determinants of such traits are difficult to identify since the trait or disease results from a set of genetic polymorphisms that may be common within the population, both affected and non-affected. The interplay of these genetic polymorphisms at different loci with environmental factors leads to the manifestation of such complex traits. Some approaches to analyzing complex traits using external apical root resorption as an example are reviewed.