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An example of how the liability threshold works can be seen in individuals with cleft lip and palate. Cleft lip and palate is a birth defect in which an infant is born with unfused lip and palate tissues. An individual with cleft lip and palate can have unaffected parents who do not seem to have a family history of the disorder. [citation needed]
It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosome abnormality. Although polygenic disorders are the most common, the term is mostly used when discussing disorders with a single genetic cause, either in a gene or chromosome.
The following is a list of genetic disorders and if known, type of mutation and for the chromosome involved. Although the parlance "disease-causing gene" is common, it is the occurrence of an abnormality in the parents that causes the impairment to develop within the child. There are over 6,000 known genetic disorders in humans.
Candida albicans infection; Candida parapsilosis infection; Cytomegalovirus infection; diphtheria; human coronavirus infection; respiratory distress syndrome; measles; meconium aspiration syndrome
Traits controlled by two or more genes are said to be polygenic traits. Polygenic means "many genes" are necessary for the organism to develop the trait. For example, at least three genes are involved in making the reddish-brown pigment in the eyes of fruit flies. Polygenic traits often show a wide range of phenotypes.
Congenital Disorder of Glycosylation (CDG) Congenital hyperinsulinism; Congenital insensitivity to pain with anhidrosis (CIPA) Congenital pulmonary airway malformation (CPAM) Conjoined twins; Costello syndrome; Craniopagus parasiticus; Cri du chat syndrome; Cyclopia; Cystic fibrosis
A polygene is a member of a group of non-epistatic genes that interact additively to influence a phenotypic trait, thus contributing to multiple-gene inheritance (polygenic inheritance, multigenic inheritance, quantitative inheritance [1]), a type of non-Mendelian inheritance, as opposed to single-gene inheritance, which is the core notion of ...
Polygenic adaptation describes a process in which a population adapts through small changes in allele frequencies at hundreds or thousands of loci. [ 1 ] Many traits in humans and other species are highly polygenic , i.e., affected by standing genetic variation at hundreds or thousands of loci.