Pedigree analysis is the classic method of human genetics. Pedigree is a family history of hereditary condition or diagram of a family history indicating the family members, their relationships to proband, and their status with respect to a particular hereditary condition.
Following symbols are used for study-
- A pedigree includes two generations of ascent from the consultant (the person requesting medical or genetic information) or proband (the affected individual that brings family to medical attention), and two generations of descent.
- Information is collected on first-degree relatives (children, siblings and parents), second-degree relatives (half siblings, aunts, uncles, nieces, nephews, grandparents and grand children), and sometimes third-degree relatives (e.g. first cousins)
- The first step in pedigree analysis is to observe the number and relationships of all individuals who express the same or similar clinical features.
- Second step is to evaluate the status of family members in the pedigree
- The third step is to calculate the risk
- For those traits exhibiting dominant gene action:
- affected individuals have at least one affected parent
- the phenotype generally appears every generation
- two unaffected parents only have unaffected offspring
- And for those traits exhibiting recessive gene action:
- unaffected parents can have affected offspring
- affected progeny are both male and female
- An autosomal disease can usually be distinguished by seeing male-to-male transmission of mutation, but since males pass only the Y chromosome to their sons, there should never be father to son transmission of an X-linked gene.
- Males will be most commonly affected in an X-linked disease, whereas males and females should be equally affected in autosomal disorders.
- A dominant disease will be seen in approximately half of the individuals in each generation, but recessives occur very rarely.
- If the mutation is in the mitochondrial genome, affected mothers will pass the trait to all of their children, but none of the offsprings of an affected male should have the disease.
- By carefully observing the position of affected individuals, mutation carriers may be identified. From this data, the risk of carrier status for other family members or the chance that a couple may have an affected child can be estimated.
- pedigree is an important method of establishing patient rapport,
- serves as a visual demonstration for providing patient education (e.g., variation in disease expression in a family),
- identifying order or relatives at risk for disease or who can be informative for inclusion in genetic research.
- to identify inherited traits and infer patterns of transmission.
- method used in genetic diagnosis and research.
- helps the researchers to determine if a trait is Mendelian.
- helps establish the mode of inheritance.
- it can be used in segregation analysis, heritability, calculation of in- breeding coefficients and in studies of linkage.
- to determine if the disorder is dominant or recessive, autosomal or X-linked
Its usefulness will continue to develop with the rising knowledge of molecular, bioinformatics and proteomic tools.