Name(s) of analyst(s):__________________________________
Date:________________

        CASE 1: Marfan Syndrome

Marfan syndrome is caused by a single dominant allele "M" located on chromosomes #8. The recessive allele "m" codes for the normal protein fibrillin which is produced in many of the body's connective tissues. Marfan syndrome is also known as "spider disorder" because people with the gene commonly have long, slender fingers. Other symptoms include
abnormalities of the heart, blood vessels, lungs, eyes, bones and ligaments. Arm and legs may be unusually long in
proportion to the torso and the individual's joints may be abnormally loose. Symptoms may be severe or mild, and may be
present at birth or show up in adult life. The disorder sometimes causes sudden death in adults who were unaware that
they had the disease. Flo Hyman, a member of the U.S. 1984 silver medalist volleyball team, died seconds after coming
out of a 1986 game during a routine substitution. Marfan syndrome affects approximately 20,000 people in the United
States, including males and females of any race or ethnic group. Researchers are currently working on a test that could
detect the presence of the Marfan's gene in utero before birth.

Bill, whose father died of Marfan syndrome, married Betty who has no history of the disease in her family. The couple
would like to start a family but are concerned that their child might inherit the defective gene for Marfan's. Bill and Betty
have come to you for some advice. You will be expected to present them with some possible solutions to their problem.
Include the following in a well-organized report to Billy and Betty:

a. Bill and Betty's possible genotypes and phenotypes (assume Bill has inherited the defective gene).
b. The percentages of possible genotypes and phenotypes of their offspring given the information in Part "a" above. Show
    all work.
c. Create a pedigree chart that show a diagram of Bill and Betty's offspring.
 

      CASE 2: Cystic Fibrosis

Cystic fibrosis (CF) is the most common lethal genetic disease. Individuals must be homozygous for the recessive "f"
allele in order to inherit cystic fibrosis. Symptoms of CF include inadequate pancreatic function and severe fluid
accumulation in the lungs and respiratory tract due to defective chloride pumps. If untreated, offspring inheriting the
disease die by the time they are 4 or 5 years old. A special diet and antibiotics to prevent infection can increase the
longevity of individuals with cystic fibrosis to an average of 27 years.

Hank and Lydia are concerned that they might have a child with cystic fibrosis. Hank and Lydia each had a brother that
died as a result of CF. From the information about their brothers, you deduce that both parents of Hank and both parents
of Lydia must have been carriers of the recessive allele. Therefore, Hank and Lydia are offspring of monohydrid crosses.
Both Hank and Lydia are healthy and would like to know the probability that their offspring will be healthy.

Include the following in a well organized report to Hank and Lydia:

a. Possible genotypes for Hank and Lydia.
b. The probability that Hank is a carrier for cystic fibrosis and the probability that Lydia is a carrier.
c. The probablility that a child born to two carriers will have cystic fibrosis.
d. The total probability that Hank and Lydia will have a child with CF.
e. Create a pedigree chart that shows a diagram of the possible offspring of Hank and Lydia.
 

      CASE 3: Ducenne's Muscular Dystrophy

Duchenne's Muscular Dystrophy (MD) is caused by a sex-linked recessive gene "Xm" that codes for a defective muscele
protein. The dominant allele "XM" codes for the normal functional protein called dystrophin. The disease has its onset in
early childhood, usually 5 to 8 years, and often leads to death in the second or third decade of life. The muscles first
seem to swell and then shrink as the disease destroys more and more of the muscle tissue.

Sally and Dave, both in their late twenties, are getting married next year. Sally's younger brother, Sam, is confined to a
wheelchair and respiration machine due to MD. Her older brother, Joe, died a few years ago as a result of MD. Dave's
entire family has never heard of muscular dystrophy except for the telethon on TV each September. Sally and Dave come
to you for advice about whether they should plan on having children, adopt children, or seek prenatal testing for any
children they may conceive.

Include the following in a well organized report to Sally and Dave:

a. Dave's possible genotype(s).
b. Sally's possible genotype(s).
c. Punnett square(s) to show the probability that they will have a child with MD
d. The chance that MD could afflict their male children
e. The chance that MD could affict their female children.
 

      COMMENTARY:

a. What are the pros and cons on the issue of genetic testing for diseases? Make a chart that lists two advantages and
    two disadvantages for developing and using a test that would detect the presence of a defective gene. Think about when
    you would want to know you had the gene for the disease and when you would not want to know.
b. What is an appropriate role for genetic counselors in terms of helping couples reach parenthood decisions?