Multifactorial inheritance means that many factors (multifactorial) are involved in causing a health problem. The factors are usually both genetic and environmental, where a combination of genes from both parents, in addition to unknown environmental factors, produce the trait or condition. Multifactorial traits do recur in families, because they are partly caused by genes and shared environmental factors. 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 share a certain percentage of genes in common, depending on their relationship. For example:
|Degrees of Relationship||Percentage of Genes in Common||Example|
|First-degree relative||50 percent||parents, children, siblings|
|Second-degree relative||25 percent||aunts, uncles, nieces, nephews, grandparents|
|Third-degree relative||12.5 percent||first cousins|
An example of a multifactorial trait is height. Some people may be exceptionally short or exceptionally tall, often due to an alteration (mutation) in a single gene that has a major effect on height. However, most of the time, a child's height is similar to, or somewhere between, the parents' height. Some cancers cluster in families as the result of a combination of genetic and shared environmental factors (multifactorial influences). In such cases, generally speaking, the closer in relation a family member with cancer is to you (i.e., 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 develops cancer (or other disease) than if your second cousin develops the disease.
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