Interpreting Pedigree chart to recognize pattern of inheritance

One of the problem faced by students is solving a pedigree chart and recognizing pattern of inheritance, which is even important in day to day clinical practice.

Inheritance that needs to be differentiated in pedigree can be

Mendelian ( Single Gene defect )
Autosomal Dominant
Autosomal Recessive
X linked

Non traditional inheritance like
Mitochondrial inheritance

In a Step Wise approach

1. Identify whether pattern of inheritance is Autosomal or Sex linked.
If only Males are affected , it is likely X linked inheritance ( Recessive, X linked dominant disorders are very rare)
If both males and females are equally affected, it is Autosomal inheritance

2. Determine whether the disorder is dominant or recessive.
If only Affected parent transmit the disease , it is Dominant disorder
If non-affected parent transmit the disease, it is Recessive disorder.
In other words,
If the disorder is dominant, one of the parents must have the disorder.
If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

If disease skips generations, it is likely Recessive disorder.

Rules of Inheritance: Understanding Mendelian disorder by Dr Sulabh Shrestha

Understanding Mendelian inheritance – Epomedicine


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