All in the family

Curly hair, dimpled cheeks, brown eyes and athletic ability — these traits run in families. So does the risk of certain diseases.

Almost all diseases have a genetic component. Most diseases — including heart disease and diabetes — result from mutations in multiple genes, combined with environmental factors. Some conditions, such as Down syndrome, are caused by too many or too few genes. And some are caused by a mistake in a single gene.

Single-gene disorders are passed from generation to generation according to straightforward, predictable patterns of inheritance. Understanding these patterns will help you understand the risk of you or your child inheriting one of these disorders. These risks are the same in each pregnancy.