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Structure of DNA – the blueprint of all organisms

Deduction of Human migrations and Ancestry through the use of Uniparentally inherited DNA

Our genome is made up of 22 pairs of autosomes and 2 sex chromosomes making up a total of 46 chromosomes. We inherit half from our mother and the other from our father. If you receive an X from both your parents, you will become a female; and if you receive a Y from your father (you will always receive an X from your mother) you will be male. This makes the Y chromosome (excluding the pseudo-autosomal regions) the only nuclear chromomosome which is uniparentally inherited (males inherit it only from their fathers and females do not have it). Because it does not have a homologous pair (like the autosomes do), recombination does not occur thus no mix up of DNA sequences occur. This is why it is unique in the way that fathers pass on the same DNA sequence to their sons without any change (except for a few spontaneous mutations). So if we could go back in time and check the DNA sequence of the Y chromosome of your grandfather 20 generations back we would see that you have the same as his (apart from minor changes). This is why information through the analysis of the DNA sequence in the non-recombining regions can be used to deduce an individual’s ancestry (Jobling and Tyler Smith, 2003).

Information from the Non-recombining regions of the Y Chromosome

The Y chromosome of many males from all world populations have been analysed and a phylogenetic tree which is rooted to Africans has been constructed (Karafet et al 2008). The same is true for the mitochondrial DNA also (van Oven and Kayser, 2008). Each branch of the tree is called a ‘haplogroup’ which is the term used to describe a group of individuals who share the same Y-DNA haplotypes (or mitochondrial haplotypes in terms of the mtDNA phylogenetic tree), thus share a common ancestor some time in history (Underhill and Kivisild 2008).

European males usually belong to one of the two major Y-DNA haplogroups: R and I (see eupedia.org)

R is by far the most prevalent accounting to over 70% of males in Europe and I accounts for just over 20% (see eupedia.com for more information). What is intriguing however is that, through the analysis of the frequencies of the haplogroups in different regions of the world, haplogroup I seems to correspond to native Europeans whereas the R haplogroup seems to have arrived from Anatolia where present day Turkey is.

To conclude, there is definitely strong evidence that most European males share a common ancestor who lived in Turkey quite a few centuries ago. Human history is an intriguing area and genetics has a lot to offer to these studies!

Same for European languages?

For more information (ordered to help understand the issue better):

– Human Genome: http://en.wikipedia.org/wiki/Human_genome

– Y chromosome: http://en.wikipedia.org/wiki/Y_chromosome

– Mitochondrial DNA: http://en.wikipedia.org/wiki/Mitochondrial_DNA

– Origins, age, spread and ethnic association of European haplogroups and subclades: http://www.eupedia.com/europe/origins_haplogroups_europe.shtml

– Underhill PA, Kivisild T. 2007. Use of y chromosome and mitochondrial DNA population structure in tracing human migrations. Annu Rev Genet. 2007;41:539-64.

– Jobling MA, Tyler-Smith C. 2003. The human Y chromosome: an evolutionary marker comes of age. Nat Rev Genet. 2003 Aug;4(8):598-612.

– Karafet TM et al. 2008. New binary polymorphisms reshape and increase resolution of the human Y chromosomal haplogroup tree. Genome Res. 2008 May;18(5):830-8. Epub  2008 Apr 2.

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