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Genetic Heterogeneity
Genetic heterogeneity describes genetic variation from the normal population. Clinically, genetic heterogeneity refers to diseases that result from multiple gene abnormalities. Multiple gene abnormalities are seen in disorders such as autism, cystic fibrosis, and retinitis pigmentosa.

Role in medical disorders
Genetic Heterogeneity is responsible for the presence of many medical disorders in humans. Heritable diseases are a result of a genotype that varies from the population standard. In relation to diseases, one gene mutation (varying from population) can cause a phenotypic disorder. The mutation can be expressed differently in different individuals. Additionally, mutations in multiple genes can result in phenotype of one disorder.<ref

Occurrence
Genetic heterogeneity is present in many disorders. Multiple gene abnormalities are seen in disorders such as autism, cystic fibrosis, and retinitis pigmentosa. An inherited predisposition for the development of breast cancer has been investigated. Multiple alleles are involved in this disease.

Mechanisms of mutations
Allelic heterogeneity means that different mutations within a single gene locus (forming multiple alleles of that gene) cause the same phenotypic expression. For example, there are over 1000 known mutant alleles of the CFTR gene that cause cystic fibrosis.

Locus heterogeneity means that variations in completely unrelated gene loci cause a single disorder. For example, retinitis pigmentosa has autosomal dominant, autosomal recessive, and X-linked origins. However, only one mutant locus is needed for the phenotype to manifest.