Whither the genotype-phenotype relationship? An historical and methodological appraisal

Area of Science:

• Genetics and Behavioral Science
• Epidemiology

Background:

• The terms genotype and phenotype, proposed over a century ago, are fundamental to studying heredity.
• Inferring causality from genotype to phenotype is complicated by pleiotropy and the many-to-one genotype-phenotype relationship.
• Behavioral phenotypes, particularly aberrant ones, are multidimensional and challenging to define operationally.

Purpose of the Study:

• To explore alternative approaches for establishing valid genotype-phenotype relationships.
• To investigate the utility of endophenotypes in identifying genes associated with complex behavioral phenotypes.
• To review causal modeling techniques in genetic epidemiology, including Mendelian randomization.

Main Methods:

• Review of historical and contemporary approaches to genotype-phenotype relationship studies.
• Discussion of endophenotype concept and its limitations.
• Examination of path analysis and Mendelian randomization in genetic epidemiology.

Main Results:

• Endophenotypes offer a potential pathway to detect genes but face challenges in operational definition and empirical success.
• Mendelian randomization has shown success in identifying genotypes associated with diseases like diabetes and cancer.
• Shortcomings exist in genetic markers for intermediate phenotypes, though statistical remedies are available.

Conclusions:

• Careful consideration of causal models is essential for genetic researchers.
• Innovative statistical procedures can address limitations in identifying genetic markers for intermediate phenotypes.
• Advancements in causal inference are critical for understanding the genetic basis of complex traits and diseases.