Pedigree analysis problem with solution (example 13)

Pedigree analysis problem with solution (example 13)

Q) The following pedigree shows the inheritance of ataxia, a rare neurological disorder characterized by uncoordinated movements. Is ataxia caused by a dominant or a recessive allele? Explain.

Answer: The trait is caused by a Dominant allele


  • The trait appears in every generation ( No skipping of generations)
  • Nearly every affected individual has an affected parent.

The exception IV-2 individual had a father who carried the ataxia allele but did not manifest the trait. This shows incomplete penetrance.

A disease is said to show incomplete penetrance when some individuals express the associated trait while others do not even though they carry the disease causing gene.





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