Quantitative genetics and complex trait analysis in humans; the genetic basis of complex diseases

Ultimately, the goal of genetics is the analysis of the genotype of organisms. But the genotype can be identified – and therefore studied – only through its phenotypic effect. This means that two genotypes are recognised as different from each other because the phenotypes of their carriers are different. A problem can be seen with this approach as the actual variation between organisms is usually quantitative, not qualitative. Many different genotypes may have the same average phenotype. At the same time, because of environmental variation, two individuals of the same genotype may not have the same phenotype. This lack of a one-to-one correspondence between genotype and phenotype obscures underlying Mendelian genetics. I am going to explore the use of various statistical techniques for studying quantitative traits with application to behavioural traits. I am also going to examine whether there are behavioural traits with sufficiently high heritabilities to give hope for gene searches and I am going to discuss the difficulties that confront molecular geneticists regarding psychiatric genetics.