Joseph and Jenny have come to a genetic counselor to determine their chances of having a child with myotonic dystrophy, a degenerative muscular disorder that appears at about 50 years of age and is inherited with the autosomal dominant allele D. The autosomal recessive allele d does not contribute to the development of the disease. Both Joseph and Jenny are in their thirties and neither shows any signs of the disease at present. Jenny’s grandmother (her father’s mother) has the disease. Jenny’s grandmother’s father (Jenny’s great-grandfather) did not have the disease. There is no history of myotonic dystrophy in Joseph’s family or in Jenny’s mother’s or paternal grandfather’s family. a. Draw the pedigree that shows the familial relationships described in the
paragraph above. Use a circle to denote a woman, a square to denote a
man and a filled symbol to show individuals who have myotonic
dystrophy. In this pedigree, you are attempting to trace the inheritance of
the D allele. Beneath each symbol, show the genotype of each individual
as far as it is known. You may use blanks to indicate that part of the
genotype is unknown, if applicable.
b. What is the probability that Jenny is a carrier of the D allele?
c. What is the probability that Joseph and Jenny will have a child with
myotonic dystrophy?
d. Out of 3 children born to Joseph and Jenny, what is the probability that 1
will have myotonic dystrophy?
e. Out of 5 children born to Joseph and Jenny, what is the probability that at
least one will have myotonic dystrophy?