What Is the Pattern of Inheritance?
Genetic traits that cause a particular health condition track back to a pattern of inheritance, also called a mode of inheritance. The major types of inheritance patterns include single gene inheritance, mitochondrial inheritance and multifactoral inheritance. Associated conditions include Huntington's disease and cystic fibrosis.
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Single Gene Inheritance
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Mutations of a single gene come via autosomal or x-linked inheritance. Each type may come in recessive or dominant form. Autosomal inheritance means an autosome houses the mutated gene. Autosomes are the 22 paired chromosomes that have no involvement in sex determination. X-linked inheritance requires that the X sex chromosome house the mutation. Males have one X chromosome and females have two. Whether the inheritance is dominant or recessive depends on the number of copies of mutant allele. One mutant allele indicates recessive inheritance while two equal dominant inheritance.
Autosomal Single Gene Inheritance
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Autosomal dominant inheritance occurs when an individual has one each of normal and mutated copies. Males and females have an equal 50 percent chance of inheriting the mutated copy. Conditions caused by autosomal dominance include Huntington's disease and acondroplasia, a form of dwarfism that produces short limbs.
For an autosomal recessive condition to be present, two mutated allele copies are required. No gender difference exists in inheritance patterns. The mating of two mutation carriers produces children with a 25 percent chance of affected inheritance but a 50 percent chance of becoming an unaffected carrier. Autosomal recessive inheritance causes cystic fibrosis.
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X-linked Single Gene Inheritance
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X-linked recessive mutations do not show up in the presence of a healthy allele copy. Males have a lone X chromosome and thus present the recessive trait. Females, though rarely affected, can present if they have two mutated allele copies. Familial inheritance passes from mother to either son or daughter. Fathers can only pass to their daughters. The daughter will only inherit one mutated copy from her father. The condition Hemophilia A links to X-linked recessive single gene inheritance.
Mitochondrial Inheritance
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Mitochondrial inheritance, also called maternal inheritance, comes from the genes in mitochondrial DNA. Mitochondria are only produced by females and any associated mutations may be passed from mother to her sons or daughters. The condition Leber hereditary optic neuropathy passes through mitochondrial inheritance. Heart, liver and kidney diseases frequently have ties to mitochondrial inheritance.
Multifactoral Inheritance
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Multifactoral inheritance occurs when more than one gene mutation combines with factors such as environmental exposure or diet to increase a person's propensity for certain conditions. Heart disease exacerbated by poor diet and a lack of exercise can be an example of multifactoral inheritance. Pinning down the genetics of this inheritance is more difficult than in the more precise forms.
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