Genetic heterogeneity
Encyclopedia
Genetic Heterogeneity is a phenomenon in which a single phenotype
or genetic disorder may be caused by any one of a multiple number of alleles or non-allele (locus
) mutations. This is in contrast to pleiotropy
, where a single gene may cause multiple phenotypic expressions or disorders. Genetic heterogeneity can be classified as either "allelic" or "locus".
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.
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
or genetic disorder may be caused by any one of a multiple number of alleles or non-allele (locus
Locus (genetics)
In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
) mutations. This is in contrast to pleiotropy
Pleiotropy
Pleiotropy occurs when one gene influences multiple phenotypic traits. Consequently, a mutation in a pleiotropic gene may have an effect on some or all traits simultaneously...
, where a single gene may cause multiple phenotypic expressions or disorders. Genetic heterogeneity can be classified as either "allelic" or "locus".
Allelic heterogeneity
Allelic heterogeneity
Allelic heterogeneity is the phenomenon in which different mutations at the same locus cause the same disorder. For example, β-thalassemia may be caused by several different mutations in the β-globin gene. It is a type of genetic 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
Cystic fibrosis
Cystic fibrosis is a recessive genetic disease affecting most critically the lungs, and also the pancreas, liver, and intestine...
.
Locus heterogeneity means that variations in completely unrelated gene loci
Locus (genetics)
In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
cause a single disorder. For example, retinitis pigmentosa
Retinitis pigmentosa
Retinitis pigmentosa is a group of genetic eye conditions that leads to incurable blindness. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not become legally blind until their 40s or 50s and retain some...
has autosomal dominant, autosomal recessive, and X-linked origins. However, only one mutant locus is needed for the phenotype to manifest.