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Example of a pedigree chart using Ahnentafel numbering

A pedigree chart is a diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next,[1][2][3] most commonly humans, show dogs,[4] and race horses.

The word pedigree is a corruption of the French "pied de grue" or crane's foot, because the typical lines and split lines (each split leading to different offspring of the one parent line) resemble the thin leg and foot of a crane.

Contents

PropertiesEdit

A pedigree results in the presentation of family information in the form of an easily readable chart. Pedigrees use a standardized set of symbols, squares represent males and circles represent females. Pedigree construction is a family history, and details about an earlier generation may be uncertain as memories fade. If the sex of the person is unknown a diamond is used. Someone with the phenotype in question is represented by a filled-in (darker) symbol. Heterozygotes, when identifiable, are indicated by a shade dot inside a symbol or a half-filled symbol.

Relationships in a pedigree are shown as a series of lines. Parents are connected by a horizontal line and a vertical line leads to their offspring. The offspring are connected by a horizontal sibship line and listed in birth order from left to right. If the offspring are twins then they will be connected by a triangle. If an offspring dies then its symbol will be crossed by a line. If the offspring is still born or aborted it is represented by a small triangle.

Each generation is identified by a Roman numeral (I, II, III, and so on), and each individual within the same generation is identified by an Arabic numeral (1, 2, 3, and so on). Analysis of the pedigree using the principles of Mendelian inheritance can determine whether a trait has a dominant or recessive pattern of inheritance. Pedigrees are often constructed after a family member afflicted with a genetic disorder has been identified. This individual, known as the proband, is indicated on the pedigree by an arrow.[5] These changes may occur yearly or monthly.

In human useEdit

 
This pedigree has a sex-linked recessive disorder. It is possible to tell the trait is recessive because it skips a generation with only carriers in generation 2. Because the trait is sex-linked only females can be carriers since only females have 2 x chromosomes. As a result a lot more males tend to display sex-linked recessive disorder than females. Female carriers tend to give the trait to about half of their sons and daughters but only the sons will be affected while the daughters will only be carriers.
 
This pedigree has a sex-linked dominant disorder. It is possible to tell it is dominant because it doesn't skip generations. It is possible to tell it is sex-linked because affected fathers will pass the trait on to all of their daughters. This is because they have to pass along their affected dominant x but none of their sons because they pass on a y to their sons. The affected mother in the second generation is heterozygous (having a dominant and a recessive allele) will have a 50% chance of passing the trait on to all of her children regardless of their gender.
 
This pedigree has an autosomal dominant disorder. It is possible to tell the trait is dominant because it never skips a generation and there are no unaffected carriers. Affected children must have affected parents. When one parent possesses the trait and is heterozygous ( possessing a dominant and recessive allele) approximately half of the children will possess the dominant disorder.
 
This pedigree has a autosomal recessive disorder. It is possible to tell this order is recessive because it skips generations with none of generation 3 actually displaying the trait. When both parents display the disorder all of their kids have to display the disorder. But when only one parent displays the disorder all of the kids will be carriers but unaffected by the trait. It is possible to tell the trait is autosomal because it affects females and males equally.

In England and Wales pedigrees are officially recorded in the College of Arms, which has records going back to the Middle Ages, including pedigrees collected during roving inquiries by its heralds during the sixteenth and seventeenth centuries. The purpose of these heraldic visitations was to register and regulate the use of coats of arms. Those who claimed the right to bear arms had to provide proof either of a grant of arms to them by the College, or of descent from an ancestor entitled to arms. It was for this reason that pedigrees were recorded by the visitations. Pedigrees continue to be registered at the College of Arms and kept up to date on a voluntary basis but they are not accessible to the general public without payment of a fee.

More visible, therefore, are the pedigrees recorded in published works, such as Burke's Peerage and Burke's Landed Gentry in the United Kingdom and, in continental Europe by the Almanach de Gotha.

A pedigree may be used to establish the probability of a child having a particular disorder or condition. It may be used to discover where the genes in question are located (x, y, or autosome chromosome), and to determine whether a trait is dominant or recessive. When a pedigree shows a condition appearing in a 50:50 ratio between men and women it is considered autosomal. When the condition predominantly affects males in the pedigree it is considered x-linked.[6]

Some examples of dominant traits include: male baldness, astigmatism, and dwarfism. Some examples of recessive traits include: small eyes, little body hair, and tall stature.[7]

In animal husbandryEdit

 
Pedigree of horse Shagya IX b. 1895

In the practice of selective breeding of animals, particularly in animal fancy and livestock, including horses, pedigree charts are used to track the ancestry of animals and assist in the planning of suitable breeding programs to enhance desirable traits. Breed registries are formed and are dedicated to the accurate tracking of pedigrees and maintaining accurate records of birth, death and identifying characteristics of each registered animal.[8]

See alsoEdit

ReferencesEdit

  1. ^ pedigree chart Genealogy Glossary - About.com, a part of The New York Times Company.
  2. ^ "HELP - Ancestral File - Pedigree Chart". familysearch.org. Retrieved 6 April 2018.
  3. ^ Documenting Your Pedigree Chart By Melody Daisson - GeneaSearch.com
  4. ^ http://www.akc.org/reg/pedigree_overview.cfm
  5. ^ Michael R. Cummings "Human Heredity Principles and issues" pg 59-60
  6. ^ http://isite.lps.org/cbittle/web/documents/PedigreeCharts.pdf
  7. ^ http://www.sciencebrainwaves.com/blogs/biology/genetics/dominant-and-recessive-genes-in-humans/
  8. ^ http://research.vet.upenn.edu/pennhip/OwnerBreederInformation/SelectiveBreeding/tabid/3350/Default.aspx