Homoplasmy
Encyclopedia
Homoplasmy is the presence of a mutation
affecting all of the mitochondrial DNA
(mtDNA) copies in a mammalian cell or chloroplast DNA in a plant cell. However, when a mutation occurs, it only affects some of the mitochondria, but not all of them known as heteroplasmy. Since there are hundreds or even thousands of mtDNA copies in every eukaryotic cell, mutations may either be present in all copies (homoplasmy) or affect only a fraction of them (heteroplasmy
). Homoplasmy may also refer to the presence of mutation, or insertion of a foreign gene, into all of the plant plastid
organelles DNA (e.g. all chloroplasts). Homoplasmy, more generally, is the state whereby all non-nuclear genomes are the same, whether wild type
or mutated.
A mutation load needs to be present before disease occurs, which is called the "Threshold effect." This load is generally 80% or above mutated mitochondria in a given cell. Mitotic segregation may affect the mutant mtDNA among the daughter cells. Bottom line, in order to get mitochondrial disease you need to have certain % (usually above 80%) of mutant mtDNA to show the phenotype.
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
affecting all of the mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
(mtDNA) copies in a mammalian cell or chloroplast DNA in a plant cell. However, when a mutation occurs, it only affects some of the mitochondria, but not all of them known as heteroplasmy. Since there are hundreds or even thousands of mtDNA copies in every eukaryotic cell, mutations may either be present in all copies (homoplasmy) or affect only a fraction of them (heteroplasmy
Heteroplasmy
Heteroplasmy is the presence of a mixture of more than one type of an organellar genome within a cell or individual...
). Homoplasmy may also refer to the presence of mutation, or insertion of a foreign gene, into all of the plant plastid
Plastid
Plastids are major organelles found in the cells of plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell...
organelles DNA (e.g. all chloroplasts). Homoplasmy, more generally, is the state whereby all non-nuclear genomes are the same, whether wild type
Wild type
Wild type refers to the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard, "normal" allele at a locus, in contrast to that produced by a non-standard, "mutant" allele...
or mutated.
A mutation load needs to be present before disease occurs, which is called the "Threshold effect." This load is generally 80% or above mutated mitochondria in a given cell. Mitotic segregation may affect the mutant mtDNA among the daughter cells. Bottom line, in order to get mitochondrial disease you need to have certain % (usually above 80%) of mutant mtDNA to show the phenotype.