inherited
Meaning of inherited: Every inherited change is genetic, but plenty of genetic changes are not inherited, and the difference decides who else is at risk.
Definition of inherited
Inherited describes a trait or condition passed from parent to child through the genetic material carried in egg and sperm. An inherited change is present from conception in every cell of the body, including the cells that will form the next generation, so it can be handed on again. Whether it produces disease depends on the change itself and on how many copies are needed.
How does inherited differ from genetic?
Genetic is the wider word. It covers any change in the DNA, whenever and wherever it happened. Inherited narrows that to changes carried in the egg or sperm that made the person, which is why they sit in every cell rather than in one patch of tissue. The distinction is not a technicality. It decides whether relatives share the risk, whether children can receive the change, and whether a blood sample or a sample of the affected tissue is the one that will show it.
| Type of change | Where it sits | Passed to children |
|---|---|---|
| Inherited, also called germline | Every cell, received from a parent | Yes |
| De novo | Every cell, but new in this person rather than present in either parent | Yes |
| Somatic | Only the cells descended from the one where it arose | No |
What patterns do inherited conditions follow?
Most fall into a handful of recognizable shapes. In a dominant pattern one altered copy of a gene is enough, an affected parent is usually apparent, and on average half of the children receive it. In a recessive pattern two altered copies are needed, so parents are typically unaffected carriers and the condition appears to come from nowhere. X linked conditions mostly affect males, who have a single X, while females carrying one altered copy are often mildly affected or unaffected. A small group is carried in the DNA of the mitochondria, the energy compartments inside cells, and passes only through the egg, so an affected father does not transmit it.
Why does carrying a change not guarantee the condition?
Two ideas explain most of the gap. Penetrance describes how often people carrying a change actually develop the associated condition, and for many changes it falls well short of everyone. Expressivity describes how differently the condition shows itself among those who do, so one relative may be severely affected and another barely. Other genes, environment and chance all feed in. This is why an inherited risk is a probability rather than a verdict, and why a result is interpreted against the family history rather than on its own. It also explains an apparent contradiction in cancer: an inherited change raises the lifetime chance of a tumor, yet the tumor itself only develops once further changes arise in a somatic cell during life.
Used in a sentence
Genetic counseling addressed whether the patient's condition was inherited or had arisen as a new genetic change.
Good to know
Not every genetic condition is inherited, since a genetic change can also arise new in an individual or occur only within certain cells of the body, distinctions that affect whether the change can be passed to future children.