The human Y chromosome is a male-specific sex chromosome. When mutations (errors in the copying process) arise in the Y chromosome, they are passed down directly from father to son in a direct male line of descent and define a tree of Y “haplogroups”. The mutations on the Y chromosome can thus be used to trace our paternal ancestors all the way back to the most recent common paternal ancestor of all men alive today, Y chromosomal Adam.
When I first got interested in genetic genealogy around 2010, I had my DNA tested by the National Genographic Project, funded by the National Geographic to collect over a million DNA samples to map the patterns of human migration across the world. This project measured mutations known as short tandem repeats (STRs) at 12 sites, and gave a statistical prediction of my Y-haplogroup, R1b (M343) and subclade R-M269. A year later I upgraded my Y-DNA analysis to 44 STRs with Ancestry.com. At the time, I decided that I would wait for the technology to improve and the cost to drop and do a more comprehensive test which would definitively determine my Y haplogroup.
And so last year I did the Big Y-700 test with FamilyTreeDNA which examines 700 short tandem repeats, and over 200,000 single-nucleotide polymorphisms(SNPs) identifying known haplogroups as well as millions of locations where there may be new branch markers on the Y chromosome. This company claims to have the world’s largest genealogical YDNA database with over 2 million people included.
A single-nucleotide polymorphism (SNP, pronounced snip) is a DNA sequence variation occurring when a single nucleotide adenine (A), thymine (T), cytosine (C), or guanine (G) in the genome differs between individuals. For example, two sequenced DNA fragments from different individuals, AAGCCTA to AAGCTTA, contain a difference in a single nucleotide. In this case we say that there are two alleles: C and T. Almost all common SNPs have only two alleles.
Although it contains ~1% of the genome length in a human male cell, the lack of recombination along most of the Y chromosome makes it relatively easy to construct the evolutionary relationships among the Y haplogroups, known as a phylogenetic tree. The most recent version of the Y chromosome phylogenetic tree is maintained by the International Society of Genetic Genealogy (https://isogg.org/tree/index.html). The human Y chromosome contains about 56 million positions or base pairs. Of them, roughly 23 million base pairs (40%) are useful for phylogenetic analysis and FamilyTree DNA has identified over 500,000 unique mutations in the Y chromosomes of their testers.
Figure 1. Migration routes of Y haplogroups dating back to Y-DNA Adam (denoted by capital Y) in West Africa around 275,000 years ago. All humans originated in Africa and migrated out, branching into the main out of Africa haplogroups, including haplogroup R predominant in Western Europe. Details of Eurasian haplogroup locations and migrations have changed somewhat from those shown on this 2010 map from Wikimedia. (Source: Chakazul Wikimedia Commons 18 Sep 2013)
The Y chromosome has regions of fast mutating STRs and stable regions with for which bias-free estimates of SNP mutations rates have been obtained. This allows relatively reliable dating of haplogroups. Additionally, increased levels of Y DNA testing along with substantial increases in sequenced Y DNA for ancient samples, has allowed major advances in understanding the origin, dispersal, and geographic spread of many haplogroups. Given the likely increase in dated ancient haplogroup samples, the detailed places and times of my paternal ancestral migration path from Y-chromosomal Adam onwards is likely to be revised in the future.
My Y DNA results show that I am a member of haplogroup R1b descended from Y-chromosomal Adam 275,000 years ago through haplogroups A1b, BT, CT, F-K, and P. The following diagram is an interesting visualization of the Y haplogroup tree with all its major branches from FamilyTree DNA.
In May 2019, the Y-DNA Haplotree passed 20,000 branches, defining over 150,000 unique haplogroups. This makes the FamilyTreeDNA Haplotree the largest and most detailed phylogenetic tree of mankind in the world. The brown area is haplogroup R, R1b is most of R so you can see R1b is a good 40-45% of the tree. This is because the majority of testers to date have European ancestry, not that R1b is the largest haplogroup in the world.
There are at least 13,267 branches on the R1b tree. My Y haplogroup is at the end of one of the branches in the group that meets the circumference where the R1 of R1b is placed. Haplogroup R1b is the most frequently occurring paternal lineage in Western Europe, accounting for 50% or more of all paternal lineages in Europe. It peaks at the national level in Wales at a rate of 92%, at 82% in Ireland, 70% in Scotland, 68% in Spain, 60% in France (76% in Normandy), about 60% in Portugal,] 45% in Eastern England, 50% in Germany, 50% in the Netherlands, 42% in Iceland, and 43% in Denmark.
In a following post, I will summarize the migration path and time line of my paternal ancestors from Y chromosomal Adam down to my most recent haplogroup-defining mutation dated to 510 AD and figure out which wave of migrants into Europe my paternal great-grandfathers were part of and where they were during the ice age.