Multifactorial Inheritance
Multifactorial inheritance means that many factors (multifactorial) are involved in
causing a health problem. The factors are usually both genetic and environmental.
A combination of genes from both parents plus unknown environmental factors make the
trait or condition. Multifactorial traits do happen in families, because they are
partly caused by genes and shared environmental factors. But they might now follow
recognizable patterns. The chance of a multifactorial trait or condition happening
to you depends on how closely the family member with the trait is related to you.
For example, the risk is higher if your parent or sibling has the trait or disease
than if your first cousin has the trait or disease. Family members have a certain
portion of genes in common, depending on their relationship. For example:
Degrees of relationship
|
Percentage of genes in common
|
Example
|
First-degree relative
|
50%
|
parents, children, siblings
|
Second-degree relative
|
25%
|
aunts, uncles, nieces, nephews, grandparents
|
Third-degree relative
|
12.5%
|
first cousins
|
An example of a multifactorial trait is height. Some people may be very short or tall,
often because of a change (mutation) in a single gene that has a major effect on height.
But most of the time, a child's height is similar to, or somewhere between, the parents'
height. Diseases such as diabetes, high blood pressure, or cancer are multifactorial.
Some cancers cluster in families as the result of a combination of genetic and shared
environmental factors (multifactorial influences). In such cases, the closer in relation
a family member with cancer is to you—the more genes you share—the higher your chance
to also develop cancer. In other words, it is more significant for your personal health
if one of your parents or siblings gets cancer or another disease than if your second
cousin gets the disease.