Create a pedigree after investigating the following family history…
At 6 years old, Johnny has started to fall down a lot. He always has a skinned knee or a bruised
elbow. He says it’s harder and harder to get up and has been a couch potato for about a year now.
When he first learned to walk he was the fastest thing in the house, but now he isn’t moving very
well. When Johnny’s mother took him to the doctor it was found that he had a high level of
creatinine phosphokinase in his blood. Johnny was diagnosed with Duchenne Muscular
Dystrophy. One of the first people that Johnny and his parents subsequently talked to was a
genetic counselor. The counselor made a pedigree of Johnny’s family. This is what the family
told the counselor:
1) Johnny has been diagnosed with Duchenne Muscular Dystrophy (DMD.) He is an only child.
2) Neither of Johnny’s parents has DMD.
3) Johnny’s mom has 1 brother and 1 sister.
4) Johnny’s dad has 1 brother and 1 sister.
5) Johnny’s Uncle Joe (mom’s brother) has DMD.
6) Johnny’s grandmother (mom’s mom) had a brother who died from DMD.
7) Johnny’s cousin Pete (mom’s sister’s son) has DMD.
8) No one ever had muscular dystrophy in Johnny’s dad’s family.
DRAW YOUR PEDIGREE! Make a key, and shade in the appropriate squares and circles.
Questions:
1) What kind of inheritance (autosomal dominant, autosomal recessive, or x-linked) was involved
in Johnny’s Duchenne Muscular Dystrophy?
2) List the people in Johnny’s family who are carriers of DMD.
3) List the people in Johnny’s family who have DMD.
4) Why are there no men who are carriers of DMD?
5) Which side of Johnny’s family likely does not carry the DMD gene?