In a particular human family, John and his motherboth have brachydactyly (a rare autosomal dominant allele causing short fingers). John’s father hasHuntington disease (another rare autosomal dominant allele). John’s wife is phenotypically normaland is pregnant. Two-thirds of people who inheritthe Huntington (HD) allele show symptoms by age50, and John is 50 and has no symptoms.Brachydactyly is 90% penetrant.a. What are the genotypes of John’s parents?b. What are the possible genotypes for John? Howlikely is John to have each of these genotypes?c. What is the probability the child will express bothbrachydactyly and Huntington disease by age 50 ifthe two genes are unlinked?d. How will your answer to part (c) change if insteadthese two loci are 20 m.u. apart?

Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
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In a particular human family, John and his mother
both have brachydactyly (a rare autosomal dominant allele causing short fingers). John’s father has
Huntington disease (another rare autosomal dominant allele). John’s wife is phenotypically normal
and is pregnant. Two-thirds of people who inherit
the Huntington (HD) allele show symptoms by age
50, and John is 50 and has no symptoms.
Brachydactyly is 90% penetrant.
a. What are the genotypes of John’s parents?
b. What are the possible genotypes for John? How
likely is John to have each of these genotypes?
c. What is the probability the child will express both
brachydactyly and Huntington disease by age 50 if
the two genes are unlinked?
d. How will your answer to part (c) change if instead
these two loci are 20 m.u. apart?

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