Pedigree

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A pedigree is a diagram used to illustrate the individual phenotypic relationships between relatives. In drawing or analyzing a pedigree, there are certain standard symbols that are used. An unfilled circle is used to represent a normal female, an unfilled square to represent a normal male and a diamond to represent a normal individual of unknown gender. In contrast, a filled or shaded circle indicates a female affected by the particular disease trait and a filled or shaded square represents an affected male. A half-filled circle shows a heterozygous female for the disease allele or alleles and a half-filled square indicates a heterozygous male for the trait. These heterozygous individuals are known as carriers of the particular disease allele or trait. An unfilled circle crossed by a line indicates a deceased female and an unfilled square crossed by a line indicates a deceased male.

Mating between males and females is shown by a horizontal line between their respective symbols. This line is then attached to another horizontal line below, which is joined to the symbols for their offspring. Siblings are depicted from left to right in the order in which they were born. The eldest sibling is shown to the far left and the youngest to the far right. Mating between family members (consanguination) is depicted by a double line between their symbols.

Numbers are frequently used in pedigrees to indicate individuals or generations. Generations are shown in Roman numerals and individuals are shown in Arabic numerals. All individuals are numbered from left to right in a pedigree.

Pedigrees can be constructed for dominant or recessive gene alleles[1].

An example of a pedigree. Pedigree symbols1.jpg

                  An example of a pedigree[2]                                                          Pedigree symbols[3]                              

References

  1. Hartl, D.L. and Ruvolo, M.(2012), Genetics : Analysis of Genes and Genomes, 8th Edition, Massachusetts: Jones and Bartlett
  2. What is a Genetic Counselor [Internet]. Indiana Network of Genetic Counselors. 2016. Available from: http://www.ingc.info/site/what-is-a-genetic-counselor/
  3. Mendelian Genetic Disorders [Internet]. ResearchGate. 2001. Available from: https://www.researchgate.net/figure/227991784_fig2_Figure-1-Pedigree-symbols-A-subset-of-symbols-commonly-used-to-illustrate-a-family

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