Explain the Difference Between Mendelian and Non-Mendelian Diseases. Using One Neuropsychiatric Disorder (Schizophrenia) Discuss the Progress Made so Far in Understanding the Genetic Architecture of That Disorder

A discussion of the Progress made so far in understanding the Genetic Architecture of Schizophrenia
Schizophrenia: An Elusive Complex Disorder

A discussion of the Progress made so far in understanding the Genetic Architecture of Schizophrenia
Mendelian diseases conform to Mendel’s laws of genetic inheritance; segregation and independent assortment. Therefore, every pair of alleles in diploid organisms, are separated during meiosis and one allele for every trait is passed onto one of the two daughter cells, independently of all other genes. Thus, depending on the recessive or dominant status of both alleles for a gene, an individual may or may not develop a simple disorder where one gene is sufficient causality (Mendel, 1865). In Schizophrenia the prevailing genetic architecture hypothesis is that of a complex disorder composed of multiple genes, environmental and epigenetic influences, a common disease with common variants. However, the failure to identify a specific set of genes and external factors has led to much speculation on the exact nature of the disorders genetic architecture, culminating in strong support for a ‘re-branding’ to a spectrum of disorders. It is theorised that from the disorder spectrum, specific disease pathologies with confirmed causal genes could be elucidated and a final classification of a number of rare diseases would prevail.
A diseases genetic architecture is the number of risk alleles, their associated effect sizes and occurrence frequency, overlaid by epistasis. To understand the genetic architecture of Schizophrenia this paper will review the disorders inheritance patterns, phenotypes, pathophysiology and neurobiological pathways, methods of genetic study, candidate genes and the various models the data support and refute.

Inheritance and Physiology
Schizophrenia has a complex mode of inheritance with a proven genetic architecture and heritability of 80%; the proportion of phenotypic variance accounted for by total genetic

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