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Pedigree Inheritance Pattern of Huntington's Disease

Please see attachment for pedigree inheritance pattern of Huntington's disease.

Huntington's disease is a late-onset disease caused by a single, dominant mutation. The following pedigree is for a family with a history of Huntington disease. Those individuals who are already suffering from the disease are shaded black. However, some additional individuals in generations II and III also have the mutant Huntington's allele and will develop Huntington disease but have not yet shown symptoms. Assume that individuals marrying into the family have no history of Huntington disease (that is, they are homozygous recessive for the gene). Also
assume that the diseased male in generation I is heterozygous for the disease gene.

(a) If individuals IIIg and IIa had a child together, what is the probability that the child would develop Huntington disease?
(b) If you were told that individual IId also developed Huntington disease, would the probability calculated in (i) change? If so, what is the new probability?


Solution Preview

We're told that Huntington's is a single dominant mutation, thus any individual expressing heterozygous or homozygous dominance for that gene will have the disease. The pedigree shades in black those individuals who already show signs and symptoms, but those which may have the gene but have not yet developed signs and symptoms are still in white.

From generation ...

Solution Summary

The Pedigree inheritance patterns of Huntington's diseases are examined.