How to Draw a Genetic Pedigree Chart

A pedigree chart is a mapping of a family tree that focuses specifically on whether or not members of the family have a genetic variation. The chart enables you to determine whether a trait is dominant or recessive, as well as if it is X-linked or autosomal. Using this information, it is possible to better determine whether a child born to a couple is likely to also have the same trait.

Things You'll Need

• Paper
• Pencil
• Ruler
• Detailed family history (the more detailed, the better)

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Instructions

• 1

  Keep each familial generation on its own row when you begin drawing the tree. For example, an individual's parents, aunts and uncles would be on the row above him; siblings and cousins would be on the same row as he; and children, nieces and nephews would be on the row beneath him.

• 2

  Use the appropriate gender shape for each member of the pedigree chart. Women are represented with a circle, and males are represented with a square.

• 3

  Use lines to show relations. A horizontal line between a circle and square shows a married couple that produced offspring. Children are represented by drawing a vertical line down from the line joining the couple, a horizontal line extending over all the children from that couple and a vertical line coming down from this line to each child.

• 4

  Use lines to denote twins, with a small alteration to the way other children are noted. Fraternal twins should be connected to the parents' offspring line with a pair of diagonal lines, so they each touch the horizontal line at the same point. In addition, a horizontal line between the two children is used to denote identical twins.

• 5

  Color in the shapes of those who have the trait you are charting.

• 6

  Check to see if the trait is dominant or recessive. A dominant trait must be had by one of the parents to be passed on, whereas a recessive trait can be passed on even when neither parent displays the trait. If any children have the trait while neither parent does, the trait is recessive.

• 7

  Determine if the trait is X-linked or autosomal. If only males have the trait, it is X-linked. If any females are affected by the trait it is autosomal.