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Understanding a pedigree

In this step you will be introduced to the meanings of the symbols and line connectors used to construct a family tree or pedigree
© St George’s, University of London
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.
SymbolDescription / Meaning
Square SymbolSquare / Male
Circle SymbolCircle / Female
Diamond SymbolDiamond / Gender unknown
Line Above SymbolLine above / Siblings
Angled Lines Above SymbolAngled lines above / Twins
Line Between SymbolLine between / Partners
Two Lines Between SymbolTwo lines between / Consanguineous (blood related) couple
Line Down SymbolLine down / Children
Shaded SymbolShaded / Affected individual
Shaded Dot SymbolA small circle inside a larger circle or square / Carrier
Line Diagonally Through SymbolLine 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?
© St George’s, University of London
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The Genomics Era: the Future of Genetics in Medicine

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