Essentials of Genetics 9th Edition by Michael Palladino William Klug, Michael Cummings, Charlotte Spencer

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To test or not to test
Thomas first discovered a potentially devastating piece of family history when he learned the medical diagnosis for his brother's increasing dementia, muscular rigidity, and frequency of seizures. His brother, at age 49, was diagnosed with Huntington disease (HD), a dominantly inherited condition that typically begins with such symptoms around the age of 45 and leads to death in one's early 60s. As depressing as the news was to Thomas, it helped explain his father's suicide. Thomas, 38, now wonders what are his chances of carrying the gene for HD, and he and his wife have discussed the pros and cons of him getting tested. Thomas and his wife have two teenaged children, a boy and a girl.
How might the preparation and analysis of a pedigree help explain the dilemma facing Thomas and his family?