3. What kinds of environmental factors might cause the Marfan syndrome gene to affect two siblings very differently?

Explanation:

Genetic disorder are greatly influenced by environment because the phenotype of an individual is the product of genotype and environment. Genotype can be influenced by the environment and a different result will be observed which could be a deviation from expected.

Genetic disorder are mostly inherited and often results from mutation.

One of the factor is nutrition, good and healthy feeding can help boost the immune system and reduce effects of some diseases. Two siblings who are not exposed to eating good diet may show different symptoms to Marfan disease based how their immune system could resist it and if one is well fed than the other thing symptoms will be more pronounced on the who lacks good nutrition.

Family - some diseased can be managed if the immediate environment such as family are not hostile but rather accept and love the affected. If one is shown more care and attention there is possibility of him or her getting over the sickness than one who is abandoned. Love should be shared equally among the affected.

Adequate treatment when not given to the two siblings can make one show the symptoms more than the other.