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Understanding a pedigree

Doctors can use a pedigree to show how genetic disorders are inherited in a family. They can use this to work out the probability that someone in a family will inherit a condition.

In order to understand the following presentations on inheritance patterns, you may find it useful to spend a few moments looking at the images below and familiarising yourselves with the meanings of the symbols and connecting lines used to draw pedigrees. We have also included a PDF version of the table in the downloads section below.

Please note: This table is best viewed in landscape mode when viewing this step on a mobile device.

Symbol Description / Meaning
Square Symbol Square / Male
Circle Symbol Circle / Female
Diamond Symbol Diamond / Gender unknown
Line Above Symbol Line above / Siblings
Angled Lines Above Symbol Angled lines above / Twins
Line Between Symbol Line between / Partners
Two Lines Between Symbol Two lines between / Consanguineous (blood related) couple
Line Down Symbol Line down / Children
Shaded Symbol Shaded / Affected individual
Shaded Dot Symbol A small circle inside a larger circle or square / Carrier
Line Diagonally Through Symbol Line diagonally through symbol / Individual is deceased

Just for fun

Try drawing your own family pedigree. If you can, go back three generations (including your own). Is your family pedigree straightforward or, like many families, more complex and challenging to draw?

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This article is from the free online course:

The Genomics Era: the Future of Genetics in Medicine

St George's, University of London

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