A few definitions may help:

Autosome: A chromosome that is not a sex chromosome and therefore carries genetic information that determines body characteristics other than sex organs.

Chromosome: A threadlike linear strand of DNA in the nucleus of the body cells that carries the genes, which carry hereditary information.

Gene: A small piece of the chromosome that determines a particular characteristic such as blue eyes or red hair. (From Greek genos means offspring.)

Dominant: Surpasses the effect of the other gene.

For every characteristic in our body we inherit a gene from each parent. For example, a child may inherit a gene from his mother for blue eyes, and a gene from his father for black eyes. His eyes will be black because the gene coding for black eyes dominates the gene for blue eyes. The Gene for blue eyes is therefore submissive or recessive and the gene for black eyes is dominant.

The inherence of Marfan is also characterized by complete non- peneterance, which means that the individual may not inherit all the features, and the features that are inherited will vary in severity between even the same family members. So if the child has a Marfan gene from one parent, he will develop Marfan syndrome even if the gene from the other parent is normal.