Traits (such as eye color or risk for disease) are passed to your children by genes. Each person has two genes for each trait. One gene is from the mother and one gene is from the father.
Autosomal dominant inheritance refers to conditions caused by changes (“mutations”) in genes located on one of the 22 pairs of autosomes. Autosomes are the numbered chromosomes that are the same in all males and females. Autosomal conditions occur in both men and women and are not related to whether a person is male or female.
A parent with an autosomal dominant disorder will pass on either a changed copy of the gene or a normal copy of the gene to each of his or her children. In general, if a child inherits the changed copy of the gene, he or she is “affected” and therefore has the disorder.
A child who inherits normal (unchanged) copies of the gene will not inherit the disorder.
A person needs to inherit only one changed copy of the gene pair in order to be affected with a specific autosomal dominant disorder. The changed copy “dominates” the pair of genes. In an autosomal dominant disorder, one changed copy from one parent causes the child to have the disorder.
A child who inherits the changed copy of the gene will have Marfan syndrome. People with Marfan can pass the changed gene to their children. A person with Marfan has a 1 in 2 (50 percent) chance of passing on the changed copy of the gene and a 1 in 2 (50 percent) chance of passing on the normal copy of the gene to each child.
So, there is a 50-50 chance that each child of a person with Marfan syndrome will inherit Marfan syndrome. This 50-50 chance is the same for each and every pregnancy.
An example of an autosomal dominant condition is Marfan syndrome. It is caused by a mutation in the fibrillin 1 (FBN1) gene. If a parent has Marfan syndrome, one copy of their FBN1 gene has a change (also called a mutation). The other copy of the FBN1 gene is normal (unchanged).
Traits (such as eye color or risk for disease) are passed to your children by genes. Each person has two genes for each trait. One gene is from the mother and one gene is from the father.
Autosomal recessive inheritance refers to conditions caused by changes (“mutations”) in genes located on one of the 22 pairs of autosomes. Autosomes are the numbered chromosomes that are the same in all males and females. Autosomal conditions occur in both men and women and are not related to whether a person is male or female.
In an autosomal recessive disorder, two changed copies of a gene are inherited—one from each of the parents—which causes the child to have the disorder. The child is called “affected” because she or he has the disorder.
A carrier has only one changed copy of the gene. They are called “carriers” of the trait because they do not show any signs of the disorder. Although they have one copy of a gene that is changed, the partner copy of the gene is working correctly, so they do not develop the disorder.
When both parents are carriers for a recessive disorder, each child has a 1 in 4 (25 percent) chance of inheriting the two changed gene copies. A child who inherits two changed gene copies will be “affected,” meaning the child has the disorder.
There is a 1 in 2 (50 percent) chance that the child will inherit one changed copy and one normal copy of the gene, and therefore be an unaffected carrier (just like the parent).
There is a 1 in 4 (25 percent) chance that the child will inherit both normal copies of a gene, and be unaffected and not a carrier.
If only one parent is a carrier and the other is not, none of the children will have the condition. But each child will have a 50 percent chance of being a carrier.
For example, cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in a gene called CFTR. If both parents are carriers, each parent can pass on the changed copy or the normal copy to their children. Children who inherit two changed copies of the CFTR gene are “affected” and have the disease cystic fibrosis.
Autosomal dominant is a pattern of inheritance characteristic of some genetic disorders. “Autosomal” means that the gene in question is located on one of the numbered, or non-sex, chromosomes. “Dominant” means that a single copy of the mutated gene (from one parent) is enough to cause the disorder. A child of a person affected by an autosomal dominant condition has a 50% chance of being affected by that condition via inheritance of a dominant allele. By contrast, an autosomal recessive disorder requires two copies of the mutated gene (one from each parent) to cause the disorder. Huntington’s disease is an example of an autosomal dominant genetic disorder.
Autosomal dominant disorder. When geneticists talk about dominant disorders, they're usually referring to those rare disorders that are caused by a spelling change in the DNA of one copy of a gene. Now because the chance of passing on the altered gene copy to each child is 50%, you typically see the disorder in each generation of the family tree. For example, you might see it in the mother. You might see it then in the mother's parent or the mother's grandparents or even aunts and uncles. Although sometimes a person with a dominant disorder can be the first person in their family to have the spelling change, disorders such as Marfan syndrome and BRCA1 hereditary breast and ovarian cancer work in this way.
URL of this page: //medlineplus.gov/genetics/understanding/inheritance/riskassessment/
When a genetic disorder is diagnosed in a family, family members often want to know the likelihood that they or their children will develop the condition. This can be difficult to predict in some cases because many factors influence a person's chances of developing a genetic condition. One important factor is how the condition is inherited. For example: Autosomal dominant inheritance: A person affected by an autosomal dominant disorder
Autosomal recessive inheritance: Two unaffected people who each carry one copy of the altered gene for an autosomal recessive disorder
X-linked dominant inheritance: The chance of passing on an X-linked dominant condition
X-linked recessive inheritance: Because of the difference in sex chromosomes, the probability of passing on an X-linked recessive disorder
X-linked: Because the inheritance pattern of many X-linked disorders is not clearly dominant or recessive, some experts suggest that conditions be considered X-linked rather than X-linked dominant or X-linked recessive. As above, the probability of passing on an X-linked disorder differs between men and women. The sons of a man with an X-linked disorder will not be affected, but all of his daughters will inherit the altered gene and may develop signs and symptoms of the condition. A woman passes on one or the other of her X chromosomes to each child. Therefore, with each pregnancy, a woman with an X-linked disorder has a 50 percent chance of having a child with the altered gene. An affected daughter may have milder signs and symptoms than an affected son.
Y-linked inheritance: Because only males have a Y chromosome, only males can be affected by and pass on Y-linked disorders
Codominant inheritance: In codominant inheritance
Mitochondrial inheritance: Mitochondria, which are the energy-producing centers inside cells, each contain a small amount of DNA. Disorders with mitochondrial inheritance
It is important to note that the chance of passing on a genetic condition applies equally to each pregnancy. For example, if a couple has a child with an autosomal recessive disorder, the chance of having another child with the disorder is still 25 percent (or 1 in 4). Having one child with a disorder does not “protect” future children from inheriting the condition. Conversely, having a child without the condition does not mean that future children will definitely be affected.
Although the chances of inheriting a genetic condition appear straightforward, factors such as a person's family history and the results of genetic testing can sometimes modify those chances. In addition, some people with a disease-causing variant never develop any health problems or may experience only mild symptoms of the disorder. If a disease that runs in a family does not have a clear-cut inheritance pattern, predicting the likelihood that a person will develop the condition can be particularly difficult.
Estimating the chance of developing or passing on a genetic disorder can be complex. Genetics professionals can help people understand these chances and help them make informed decisions about their health.
Learn how to cite this page