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.