Analysis: Consider Joe's story. IF the test shows he does have Marfan syndrome, and if he inherited the Marfan gene from his mother, does this mean that his brother and sister also have it? You may want to draw up a Punnett Square or drawing to help you explain your answer. HINT: Is there any suggestion that he got a Marfan gene from his father?

We inherit genes from our biological parents in specific ways. One way is called autosomal dominant inheritance.

What is autosomal dominant inheritance?

Autosomal dominant inheritance means that the gene in question is located on one of the autosomes. These are numbered pairs of chromosomes, 1 through 22. (These chromosomes do not determine an offspring's gender.) Dominant means that only one gene from one parent is necessary to pass down a trait or a disorder. When a parent has a dominant trait or disorder, there is a 50 percent chance that any child he or she has will also inherit the trait or disorder:

Genetic illustration demonstrating autosomal dominant inheritance

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What is Marfan syndrome?

Marfan syndrome occurs in one of 5,000 live births. It is a connective tissue disorder associated with autosomal dominant inheritance. Connective tissue is abundant in the body and is important as a supporting structure. It is especially important for the musculoskeletal system. It also provides support for other body systems as well, including the eyes and the heart. The gene for Marfan syndrome is called fibrillin-1. This gene is localized to chromosome #15 on the long arm (q) at 15q21.1.  

Common findings in individuals with Marfan syndrome include those related to connective tissue disorders. These include abnormal enlargement of the aortic root of the heart, dislocated lenses of the eyes, and a tall, lanky body with increased joint mobility, scoliosis, long flat feet, and long fingers. Findings may vary among individuals diagnosed with this condition, even within a family.

If an individual carries an abnormal gene for Marfan syndrome, that individual has a 50 percent risk of passing down the disorder to each future offspring. If a person does not carry the gene abnormality, then the risk for occurrence of the disorder in future offspring is the same as for the general population.

Explanation: