Linkage Analysis Of Pedigrees

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Pedigrees
A pedigree, which is also called a genealogy, can be formally defined as “a group of individuals together with a full specification of all the relationships among them” (Thompson, 1986). Pedigrees can be shown graphically. One example of a pedigree is shown in Figure 2.3. By convention we use a square to denote a male and a circle to denote a female. Horizontal lines below couples are used to represent marriages. Parents and their children are linked through vertical lines. The individuals who are in the same level in the pedigree are in the same generation, often denoted by Roman numerals. Each person in each generation is labelled by Arabic numbers. Individuals with data e.g. those who are affected by a disease, are shown by shading. By …show more content…

Pedigrees are often used to determine the mode of inheritance (e.g. dominant, recessive, etc.) of genetic diseases. They are also essential to linkage analysis.
Linkage analysis is the analysis of the linkage in the inheritance between genes at different loci based on the observational phenotypes and the known pedigree structure (Palmer, 2011). Linkage between loci is the tendency for alleles of two or more loci close on the chromosome to be transmitted to the next generation together. So generally the closer two genes lie on a chromosome, the more likely they will show linkage. Genes located on different chromosomes, for example, do not show linkage. Genetic linkage studies aim to estimate the distance between a set of markers (polymorphic DNA sequences with known location) and a putative trait gene by estimating the recombination fractions. If a disease tends to be passed to offspring along with specific markers, then it can be concluded that the gene(s) which are responsible for the disease are located close on the chromosome to these markers. The disease could be a Mendelian disease (caused by one gene) or a complex disease, which is caused by the action of many

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