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

5164 Words Jul 3rd, 2013 21 Pages
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
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R., 2010); * Single genetic locus * Multiple single loci * Additively combining loci
Thus implying either oligogenic or polygenic architecture, with the number of genes and extent of epistasis yet to be clarified (Owen M.J., 2005). To emulate the observed risk to relatives pattern several variants may be combined in a multiplicative way, as demonstrated by the ‘S’ curve in figure 2, where individuals with more than 43 risk alleles will develop the disorder.
Figure 2
Figure 2
Exchange models such as the liability threshold model (LTM), figure 3, can also model Schizophrenia. Both models can be created for many combinations of allele number, frequency, effect size predicting a steep rise in disease probability for a small percentage of the population. In the LTM all individuals have unknown liability with both an environmental and genetic component, presentation is sporadic, limited to those that meet the threshold.
Figure 3
Figure 3
LTM is parameterized solely on the total variance the genetic architecture is accountable for making it a good model to hypothesise upon as it requires no explicit assumptions for; allele number, frequency and effect size. LTM supports the current range of exchangeable genetic models that have varying hypothesis but limited statistical differentiation (Wray N. R., 2010). Reduced fecundity in patients decreases genetic variance whilst de novo mutations exert the opposite force, neither of which can be captured

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