Heteroplasmy

Heteroplasmy is the presence of more than one type of organellar genome ( or plastid DNA) within a cell or individual. It is an important factor in considering the severity of . Because most eukaryotic cells contain many hundreds of mitochondria with hundreds of copies of mitochondrial DNA, it is common for mutations to affect only some mitochondria, leaving most unaffected.

Although detrimental scenarios are well-studied, heteroplasmy can also be beneficial. For example, centenarians show a higher than average degree of heteroplasmy.

Microheteroplasmy is present in most individuals. This refers to hundreds of independent mutations in one organism, with each mutation found in about 1–2% of all mitochondrial genomes.

In order for heteroplasmy to occur, organelles must contain a genome and, in turn, a genotype. In animals, are the only organelles that contain their own genomes, so these organisms will only have mitochondrial heteroplasmy. In contrast, photosynthetic plants contain mitochondria and chloroplasts, each of which contains plastid genomes. Therefore, plant heteroplasmy occurs in two dimensions.

In 1909, while studying chloroplast genomes, Erwin Baur made the first observations about organelle inheritance patterns. Organelle genome inheritance differs from nuclear genome, and this is illustrated by four violations of Mendel's laws.

Vegetative segregation, the random partitioning of cytoplasm, is a distinguishable characteristic of organelle heredity. During cell division, the organelles are divided equally, providing each daughter cell with a random selection of plasmid genotypes.

Uniparental inheritance refers to the fact that, in most organisms, many offspring inherit organelle genes from only one parent. However, this is not a general law. Many organisms that have the ability to differentiate maternal and paternal sexes will produce offspring with a mixture of maternal, paternal, and biparental mitochondrial DNA.

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