How To Understand the Symbols Involved In a Pedigree Diagram
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How To Understand the Symbols Involved In a Pedigree Diagram

Pedigree is a diagram that demonstrates the genetic characteristics within a family. The genetic traits may be traced back along the generations. Interpreting the pedigree chart involves the understanding of certain symbols; which may have specific representations among the generations. The commonly used symbol of a circle and square represent the biological sex of an individual.

In genetics a chart known as pedigree illustrates genetic traits of an individual that may exist within generations. A pedigree is quite unique because it may be looked upon as a diary; in such sense that the structure of pedigree keeps track of biological traits within families.  A pedigree chart may be used to keep track of a certain gene that makes up the physical characteristics or genetic characteristics of a family.

            The structure of a pedigree appears similar to a family tree. In a pedigree diagram many generations could be shown, where generation one would be the starting generation. There are many symbols that are involved within a pedigree chart; which help interpret the chart. The square symbol and the circle symbol are used to represent the biological sex of an individual. Where the square symbol represents male and the circle symbol represents female. In order to show mating between the male and the female there is a line that connects the square to the circle. Then to show the kids of the parents, a vertical line is drawn connecting the parents to the children. The children need to be diagramed according to the birth of each. The biological sexes of the children are also represented through the usage of squares and circles. In case of twins two vertical lines forming a triangle are drawn. If the twins are identical then a full triangle is drawn, connecting the two females or two males. But in case of non identical twins a full triangle is not formed, so there isn’t a horizontal base line connection between the twins. A diamond symbol is used to show biological sex that is unidentified. In some pedigree charts there may be numbers inside the square and/or circle symbol; indicating the number of children of that sex. When it comes to looking at genetic diseases or a certain characteristic, then the individual is shaded in.  The half shaded sex symbol represents an individual who is heterozygote for a recessive trait. A mating that is represented by double horizontal lines shows consanguineous marriage.

            In order to produce a pedigree chart, it must be started off with the parent generation (generation I). Then as the mating occurs between the parents the children appear below the parent generation, which would fall under generation II. As the second generation mate, the link is carried down to the third generation. The third generation would be the grandchildren of the first generation and children of the second generation.  The generations may continue on from there, depending upon the structure of the family. Thus, looking at the pedigree chart and following through with the symbols involved in a pedigree diagram, one may trace the genetic traits within a family.

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