<P> In September 2016, scientists reported that, based on human DNA genetic studies, all non-Africans in the world today can be traced to a single population that exited Africa between 50,000 and 80,000 years ago . </P> <P> The human mitochondrial DNA is of tremendous interest to geneticists, since it undoubtedly plays a role in mitochondrial disease . It also sheds light on human evolution; for example, analysis of variation in the human mitochondrial genome has led to the postulation of a recent common ancestor for all humans on the maternal line of descent (see Mitochondrial Eve). </P> <P> Due to the lack of a system for checking for copying errors, mitochondrial DNA (mtDNA) has a more rapid rate of variation than nuclear DNA . This 20-fold higher mutation rate allows mtDNA to be used for more accurate tracing of maternal ancestry . Studies of mtDNA in populations have allowed ancient migration paths to be traced, such as the migration of Native Americans from Siberia or Polynesians from southeastern Asia . It has also been used to show that there is no trace of Neanderthal DNA in the European gene mixture inherited through purely maternal lineage . Due to the restrictive all or none manner of mtDNA inheritance, this result (no trace of Neanderthal mtDNA) would be likely unless there were a large percentage of Neanderthal ancestry, or there was strong positive selection for that mtDNA (for example, going back 5 generations, only 1 of your 32 ancestors contributed to your mtDNA, so if one of these 32 was pure Neanderthal you would expect that ~ 3% of your autosomal DNA would be of Neanderthal origin, yet you would have a ~ 97% chance to have no trace of Neanderthal mtDNA). </P> <P> Epigenetics describes a variety of features of the human genome that transcend its primary DNA sequence, such as chromatin packaging, histone modifications and DNA methylation, and which are important in regulating gene expression, genome replication and other cellular processes . Epigenetic markers strengthen and weaken transcription of certain genes but do not affect the actual sequence of DNA nucleotides . DNA methylation is a major form of epigenetic control over gene expression and one of the most highly studied topics in epigenetics . During development, the human DNA methylation profile experiences dramatic changes . In early germ line cells, the genome has very low methylation levels . These low levels generally describe active genes . As development progresses, parental imprinting tags lead to increased methylation activity . </P>

Which of the following types of dna is the most common in the human genome