On the other hand, some genetic mutations, such as those linked tohemophilia, will always manifest the disorder. Furthermore, the environment can have an effect on the degree to which a gene mutation is expressed, which explains why in some cases family members with the same genetic mutation may experience an inherited disorder somewhat differently.
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Patterns of Inheritance
The various patterns of inheritance are attributed to Austrian scientist Gregor Mendel, who discovered them while working with garden pea hybrids in the 1800s. Mendel sometimes is referred to as the father of modern genetics; likewise, the patterns of inheritance for single-gene diseases are often described as Mendelian.
According to Mendel’s work, there are five distinct patterns of inheritance: autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, and mitochondrial.
Two primary factors influence the likelihood a person will inherit a genetic disorder:Whether one copy of the mutated gene (from either parent) is passed down or whether two copies (one from both parents) are passed downWhether the mutation is on one of the sex chromosomes (X or Y) or on one of 22 other pairs of non-sex chromosomes (called autosomes)
Two primary factors influence the likelihood a person will inherit a genetic disorder:
Dominant and Recessive Genes
A genetic mutation is a change In a genetic code.
Because of the altered genetic code, the body might:
Typically, a mutation that causes an abnormal protein will result In dominant inheritance, while a mutation that causes the body to lack a protein will have a recessive disease inheritance pattern.
That’s because an abnormal product can cause harm even if the other chromosomes codes for a normal product. And if the problem with a genetic mutation is that it doesn’t code for a protein that the body needs, the normal gene on the other chromosome will usually code for the protein.
Autosomal Dominant
In autosomal dominant disorders, only one copy of a mutated gene is necessary for the disease to develop, and males and females are equally likely to be affected.
Children who have a parent who has an autosomal dominant disorder have a 50% risk of inheriting the mutated gene and developing the disorder. Examples of autosomal dominant disorders include Huntington’s disease and Marfan syndrome.
Sometimes, however, these disorders result from a new mutation and happen in people with no family history.
Autosomal Recessive
In autosomal recessive disorders, both copies of a mutated gene—one from each parent—must be present for a person to develop the disease. A person with only one abnormal copy will be a carrier, but will not have the disease.
Carriers will not have any signs or symptoms of the disorder. Carriers have a 50% chance of passing the mutation to their children.
If families in which both parents carry the mutation for an autosomal recessive disorder, the odds of the children having the disorder are as follows:
Examples of autosomal recessive disorders includecystic fibrosis, sickle cell disease, Tay-Sachs disease, and phenylketonuria (PKU).
An Overview of Sickle Cell Disease
X-Linked Dominant
In males (who have one X chromosome and one Y chromosome), a mutation in the X chromosome will cause the disorder.
Most times, males have more severe symptoms of an X-link disorder than females. However, one feature of X-linked inheritance is that fathers cannot pass on these traits to their sons.Fragile X syndromeis an example of an X-linked dominant disorder.
X-Linked Recessive
In X-linked recessive disorders, the mutated gene occurs on the X chromosome. Because males have one X chromosome and one Y chromosome, a mutated gene on the X chromosome is enough to cause an X-linked recessive disorder.
However, a female with a genetic mutation on one X chromosome is a carrier of that disorder. From a statistical standpoint, this means 50% of her sons will inherit the mutation and develop the disorder, while 50% of her daughters will inherit the mutation and become a carrier. Examples of X-linked recessive disorders are hemophilia andred-green color blindness.
What Is Hemophilia A?
Mitochondrial
Mitochondria are structures called organelles that exist in each cell of the body, where they convert molecules into energy. Each mitochondrion contains a small amount of DNA: A mutation of that DNA is responsible formitochondrial disorders.
Mitochondrial disorders are passed down from mothers to their sons or their daughters. Only females can share mitochondrial mutations with their offspring because egg cells contribute mitochondria to the developing embryo; sperm cells do not.
Conditions resulting from mutations in mitochondrial DNA can appear in every generation of a family and can affect both males and females. An example of a mitochondrial inherited disorder is Leber hereditary optic neuropathy, a form of sudden vision loss.
What Is Carney Complex?
Other Inheritance Patterns
In addition to the five main patterns of inheritance, there are a few others.
Y-Linked Disorders
Codominance
In codominance, however, both alleles are dominant and therefore phenotypes of both alleles are expressed.An example of a codominance condition isalpha-1 antitrypsin deficiency.
7 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Genetic Alliance; New York-Mid-Atlantic Consortium for Genetic and Newborn Screening Services.Appendix E: inheritance patterns. In:Understanding genetics: a New York, Mid-Atlantic guide for patients and health professionals. Genetic Alliance; 2009.National Library of Medicine: MedlinePlus.What are the different ways in which a genetic condition can be inherited?.National Library of Medicine: MedlinePlus.If a genetic disorder runs in my family, what are the chances that my children will have the condition?.New South Wales Health Education & Training Institute Centre for Genetics Education.Mitochondrial inheritance.Cleveland Clinic.Leber hereditary optic neuropathy (LHON).National Organization for Rare Disorders.Swyer syndrome.National Human Genome Research Institute.Codominance.
7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Genetic Alliance; New York-Mid-Atlantic Consortium for Genetic and Newborn Screening Services.Appendix E: inheritance patterns. In:Understanding genetics: a New York, Mid-Atlantic guide for patients and health professionals. Genetic Alliance; 2009.National Library of Medicine: MedlinePlus.What are the different ways in which a genetic condition can be inherited?.National Library of Medicine: MedlinePlus.If a genetic disorder runs in my family, what are the chances that my children will have the condition?.New South Wales Health Education & Training Institute Centre for Genetics Education.Mitochondrial inheritance.Cleveland Clinic.Leber hereditary optic neuropathy (LHON).National Organization for Rare Disorders.Swyer syndrome.National Human Genome Research Institute.Codominance.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Genetic Alliance; New York-Mid-Atlantic Consortium for Genetic and Newborn Screening Services.Appendix E: inheritance patterns. In:Understanding genetics: a New York, Mid-Atlantic guide for patients and health professionals. Genetic Alliance; 2009.National Library of Medicine: MedlinePlus.What are the different ways in which a genetic condition can be inherited?.National Library of Medicine: MedlinePlus.If a genetic disorder runs in my family, what are the chances that my children will have the condition?.New South Wales Health Education & Training Institute Centre for Genetics Education.Mitochondrial inheritance.Cleveland Clinic.Leber hereditary optic neuropathy (LHON).National Organization for Rare Disorders.Swyer syndrome.National Human Genome Research Institute.Codominance.
Genetic Alliance; New York-Mid-Atlantic Consortium for Genetic and Newborn Screening Services.Appendix E: inheritance patterns. In:Understanding genetics: a New York, Mid-Atlantic guide for patients and health professionals. Genetic Alliance; 2009.
National Library of Medicine: MedlinePlus.What are the different ways in which a genetic condition can be inherited?.
National Library of Medicine: MedlinePlus.If a genetic disorder runs in my family, what are the chances that my children will have the condition?.
New South Wales Health Education & Training Institute Centre for Genetics Education.Mitochondrial inheritance.
Cleveland Clinic.Leber hereditary optic neuropathy (LHON).
National Organization for Rare Disorders.Swyer syndrome.
National Human Genome Research Institute.Codominance.
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