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A Study of Association and Linkage of ABO Blood Types and Primary Affective Disorder
Published online by Cambridge University Press: 29 January 2018
Extract
The demonstration of either the association of a genetic marker and primary affective disorder, or linkage between a genetic marker and primary affective disorder would provide incontrovertible evidence for a genetic factor in primary affective disorder. Disease association and linkage are two separate processes. Linkage is said to occur if two genes, each responsible for a separate trait, are on the same chromosome and are close enough together that they assort in a dependent fashion. In any single family the physical proximity of two genes on the same chromosome makes it likely that the characteristics of both genes will be found in a single individual. Association, on the other hand, occurs when two genetically separate traits have a non-random occurrence in a population. Association of a disease with a specific marker may occur fleetingly on the basis of linkage. This kind of association occurs only for a few generations, so that when enough generations have passed and enough crossing over has occurred between chromosomes the association disappears. Therefore, linkage produces no permanent association in the population, but may only be found within the family. The mechanism of association is, therefore, not that of linkage, but may be more likely explained by pleiotropic effects of a single gene.
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- Copyright © Royal College of Psychiatrists, 1968
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