Mitochondria exists in the cell body and not nucleus. It is the only non-nuclear DNA in humans. Mitochondria perform an important function in the biological process of the cell. The mitochondria is identical in all the cell's of an organism and each mitochondriun is identical to all the other mitochondriun in a cell (there are many copies in each cell).
Mitochondrial DNA (often abbreviated to mtDNA) is the shortest of all the DNA strands, consisting of only around 16,000 base-pairs. By contrast, the shortest nuclear DNA (chromosome #22) is about 50 million base-pairs or more than 3,000 times the size of the mtDNA.
Because the mitochondria of the sperm cell are consumed by the egg cell during fertilization, only the egg passes mitochondria onto the offspring. Thus, the Mitochondria is passed down from a mother to a child only (not from the father). So like how yDNA passes down the patriline, mitochondria pass down the matriline. Unlike for yDNA though, the mitochondria exist in everyone and so every child has a copy of their mothers.
There is no "pair" of mitochondrial DNA like for autosomes in the nucleus. So the mitochondrial DNA does not participate in meiosis cell division (used to create eggs and sperm cells) and thus no recombination involving the mitochondria either. Thus the mitochondrial DNA is very stable for hundreds of generations. Even more so than the yDNA.
Because Mitochondrial DNA is so short, and passes from generation to generation relatively unchanged, it can really only be used for population studies to understand the movement of people's thousands to tens of thousands of years ago. The only benefit in Genetic Genealogy is that if you believe you have two people descended down the same Matriline, then they should have the same Mitochondrial DNA. You cannot differentiate people with common ancestors in the genealogical time frame like you can with yDNA or the autosomes.
Hundreds of SNP's have been identified in the Mitochondrial DNA which are used to differentiate, slightly, people within the population. Unlike shared segments of tens of thousands of SNPs used in the atxDNA analysis, there are very few SNPs to compare and understand. So single SNP value differences are considered a significant marker and indicate a difference between two individuals; like for yDNA analysis, but at a much greater time scale. See PhyloTree for an introduction and gateway to some of this work on haplogroups.
The mitochondria reference model has been developed and is distinct from the general human genome model. The mitochondria model is added to the main genome model for sequencer alignment purposes, but is usually treated somewhat separately otherwise. There have been three main models available: the (revised) Cambridge Reference System (rCRS), the Yoruba, and the RSRS. Yoruba was used for awhile in the released human genome model but has since been replaced by rCRS. RSRS, the only model based on trying to represent "Eve" (the root of the mitochondria phylogenetic tree, has never caught on or been adopted in any real form. But unlike the human genome model, the mitochondria models are all very similar and one can usually "liftover" any results from one model to the other with a high degree of confidence.
Mitochondrial DNA (often abbreviated to mtDNA) is the shortest of all the DNA strands, consisting of only around 16,000 base-pairs. By contrast, the shortest nuclear DNA (chromosome #22) is about 50 million base-pairs or more than 3,000 times the size of the mtDNA.
Because the mitochondria of the sperm cell are consumed by the egg cell during fertilization, only the egg passes mitochondria onto the offspring. Thus, the Mitochondria is passed down from a mother to a child only (not from the father). So like how yDNA passes down the patriline, mitochondria pass down the matriline. Unlike for yDNA though, the mitochondria exist in everyone and so every child has a copy of their mothers.
There is no "pair" of mitochondrial DNA like for autosomes in the nucleus. So the mitochondrial DNA does not participate in meiosis cell division (used to create eggs and sperm cells) and thus no recombination involving the mitochondria either. Thus the mitochondrial DNA is very stable for hundreds of generations. Even more so than the yDNA.
Because Mitochondrial DNA is so short, and passes from generation to generation relatively unchanged, it can really only be used for population studies to understand the movement of people's thousands to tens of thousands of years ago. The only benefit in Genetic Genealogy is that if you believe you have two people descended down the same Matriline, then they should have the same Mitochondrial DNA. You cannot differentiate people with common ancestors in the genealogical time frame like you can with yDNA or the autosomes.
Hundreds of SNP's have been identified in the Mitochondrial DNA which are used to differentiate, slightly, people within the population. Unlike shared segments of tens of thousands of SNPs used in the atxDNA analysis, there are very few SNPs to compare and understand. So single SNP value differences are considered a significant marker and indicate a difference between two individuals; like for yDNA analysis, but at a much greater time scale. See PhyloTree for an introduction and gateway to some of this work on haplogroups.
The mitochondria reference model has been developed and is distinct from the general human genome model. The mitochondria model is added to the main genome model for sequencer alignment purposes, but is usually treated somewhat separately otherwise. There have been three main models available: the (revised) Cambridge Reference System (rCRS), the Yoruba, and the RSRS. Yoruba was used for awhile in the released human genome model but has since been replaced by rCRS. RSRS, the only model based on trying to represent "Eve" (the root of the mitochondria phylogenetic tree, has never caught on or been adopted in any real form. But unlike the human genome model, the mitochondria models are all very similar and one can usually "liftover" any results from one model to the other with a high degree of confidence.
See Also
- Mitochondrial haplogroup pages at Wikipeadia and 23andMe
- Article "Characterization of mitochondrial haplogroups in a large population-based sample from the United States to get a flavor of distribution studies of such haplogroups
- Eupedia Distribution Maps of Mitochondrial Haplogroups in Europe and Africa