Y-chromosomal Adam

Adam of the Y chromosome is a label from the Archäogenetik for that primeval man, who is related to all living at a certain later date men over an unbroken lineage exclusively male offspring. A " Adam of the Y chromosome " So this is the common ancestor of all living at a particular time men, the one reconstructed if one defines ancestry exclusively on fathers and male ancestors ( paternal ), mothers and female ancestor completely ignores and more determined under this condition common ancestors of the recent genealogical selects.

The term and its significance can be derived from the fact that the Y chromosome, unlike other chromosomes is inherited exclusively from father to son. In a " Adam of the Y chromosome " is thus to the phylogenetically youngest man in the genus Homo, go back to all existing at the relevant time human Y chromosomes. He is the male counterpart to mitochondrial Eve, the historic last woman who is related to all living at a certain moment people through an unbroken line of exclusively female progeny and therefore all stem from the existing at this moment mitochondria.

Identity

Even if one assumes that all of humanity is descended from a specific first man that it has therefore been a real ancestor of all humans in the manner of Adam of the Bible, but this is not the Adam of the Y chromosome is a true. Convinced of the original Adam exactly one son, then the father's death the son of the new Adam. Convinced of the original Adam several sons, he remains initially also after his death, Adam loses this role but later on one of his descendants, as soon as all die except one of which he founded "houses", so once only by one of his sons male descendants exist. The new as well as any subsequent Adam ranging role in question continue under analogous circumstances, where theoretically every time any number of generations can be skipped.

When Adam of the Y chromosome, it must be so that neither the first man ever yet the only man of his generation to act. Although Adam of the Y chromosome is the ancestor of all living men at the relevant time, by definition, it must theoretically not necessarily the ancestor of all living at the relevant time be women. He must in principle not even be human.

Recent studies on the molecular clock and various genetic markers suggest that the current of the Y chromosome Adam lived approximately 60000-90000 years ago in Africa. He would thus Although about 85,000 years later than the current Mitochondrial Eve, but was born on the same continent.

Implications

The current state of relevant research supports the so-called out- of-Africa theory, according to which the entire humanity today is descended from a manageable and homogeneous population of African hominids. It invalidated so that the competing hypothesis that humanity today would result from a mixing of different groups of people who would have evolved independently from different geographically separate pre-human groups. The result provides no answer to the currently much-debated question of whether the current non-African ethnic groups go back to a large or several small African emigration waves.

Genetics

The Y-chromosome is not recombined than 95 % of its length with the X- chromosome. The DNA of all men must go back to a single ancestor in this area, so be monophyletic.

Compared to apes the Y chromosome shows significantly greater sequence divergence than the autosomes. For example, but the Y chromosomes of humans and chimpanzees by 1.7 %, autosomes differ on average by only 1.25 %. Within the species diversities of the Y chromosome, however, are significantly lower than for autosomes.

The Y-chromosome is inherited only the male germ line, wherein the mutation rate is somewhat higher than in the female. This explains the higher divergence of the sequences between primates.

One of the factors for the genetic diversity within the human population is the lower effective population size. It is only about ¼ of the size of autosomes and thus corresponds approximately to the mitochondrial DNA. The age of the Mitochondrial Eve and Adam of the Y chromosome must therefore be similar, but not identical, since the actual effective population sizes can vary quite.

Genetic diversity

Although the current population size of humans is far higher than the other great apes, the genetic diversity in humans is much smaller. In a study of 3,000 bases long DNA segment on the Y chromosome of 101 Commons chimpanzees and bonobos, seven were found 23 variable positions, while 42 people in the same region showed no differences among themselves. Even the orangutan shows a much higher genetic diversity than humans.

The gorilla is the only Hominoid a lower genetic diversity of the Y chromosome than humans, although its genetic diversity is much higher in mitochondrial DNA and the X chromosome. The reason is the special social structure of gorillas. They live in groups in which a dominant male ( silverback ) all mated females. This reduces the effective population size of the Y chromosome, which has its low genetic diversity result.

The diversity of the Y chromosome in humans is the highest in Africa. So it is only in Africa, the very old macro - haplogroups A and B, while another Makrohaplogruppen are found both in Africa and outside Africa. The haplogroups outside Africa are highly ramified, which is typical of expanding populations. The only apparently greater diversity of Y chromosomes in Europe and Asia due to the fact that anthropologists (eg Makrohaplogruppe F in the haplogroups G to R ) have divided the Makrohaplogruppen Eurasia in younger Unterhaplogruppen to understand and more recent settlement stages to can.

Note: Africa would also show for the Y chromosome, the highest diversity when measuring genetic diversity as the number of pairwise differences present.

Genetic pedigree

Unlike the mitochondrial DNA, the DNA sequences of the Y chromosome differ only slightly from person to person. If you wanted to generate a pedigree only by comparison of sequences, as in the Mitochondrial Eve, very long sequences would be required. This would have resulted mainly in the early 1990s, when the first studies of this kind began tremendously high costs. Instead, the researchers working with genetic markers. The first marker was discovered in 1985. Since then, more and more markers are added. The DHPLC technique makes an important contribution.

• The pedigrees clearly point to an African origin of the Y chromosome, although not as significantly as in the mitochondrial DNA.
• The two oldest branches of the tree (A and B) are virtually unique to Africa, but are only about 13 % of the Y chromosomes in Africa in these haplogroups.

The age of Adam

Estimating the time to the last common human paternal ancestors is particularly difficult. Recent studies revealed a surprisingly young age of the Adams of the Y chromosome, although with large error intervals. Thomson et al ( 2000) estimated the time to the last common ancestor to 60,000 years ( 60000-90000 ). If these results, it means that the Adam of the Y chromosome has lived only a short time before the first great exodus from Africa. This distinguishes it clearly from the Mitochondrial Eve, who lived about 175,000 years ago. The very young age of the Y chromosome would also explain why the genetic diversity in Africa is not much higher than in Eurasia and why it is so low overall in humans. It also explains why they are not so clearly separate from non- Africans in the family tree of the Y chromosome Africans, as is the case with the mitochondrial DNA.

However, a 2013 study published calculated for the Y- chromosome of an African American ( " Albert Perry " ) that it had separated themselves already 338,000 years ago by any of the Y -chromosome lines and similarities to the Y- chromosomes of a group of 11 men in the African Cameroon having.

2013 Finally, another study was published in Science, according to which the mitochondrial Eve lived 99000-148000 years ago and the " Adam of the Y chromosome " 120000-156000 years ago.

Selection

All studies on the origin of a locus as the Y chromosome implicitly assume that the locus is not under selection, ie the different haplotypes are neutral variations. Selection reduces the genetic diversity because of the advantageous Y chromosomes spread in the population and less advantageous displace. Krausz et al ( 2001) described a haplotype in Danish men, which is associated with a reduced number of sperm. A real proof for selection on the Y chromosome, there is so far not yet.