Our mitochondrial genome
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Every human
cell
has a chromosome that's not located in the nucleus but found in the cell's
energy-generating organelle, the
mitochondrion. According to the 'endosymbiont hypothesis', an ancestor
of
eukaryotic cells
incorporated an ancestor of mitochondria,
then a free-living bacterium. Subsequently, a symbiotic relationship ensued
in which the endosymbiont produced energy-rich ATP in exchange for nutrients.
Thus provided for, it shed most of its genes and lost the ability to live
independently. Today, the human mitochondrial genome consists of only 37
genes on a ring-shaped chromosome of 16,569 bp. Important genes, nevertheless,
since many diseases have been found to originate in mutations of mitochondrial
genes. |
 Mitochondrial
Mutations
consist of insertions, deletions, or single nucleotide polymorphisms (SNPs).
Mutations are common in mt DNA, due to exposure to hydroxide radicals generated
as a by-product of respiration. Mitochondrial mutations, especially mtSNPs,
can be used to retrace the maternal lineages of modern humans.
Since
most cells contain several thousand mitochondria which, in turn, contain
about ten copies of the mitochondrial chromosome, mtDNA could be isolated
from bones as old as 60,000 B.C. opening up an opportunity to
further examine the relationship between modern humans and extinct hominids,
the Neandertals.
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Scientific American Special on Human Origins
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