The runt of the litter it is as shown by the last post. Its linear array of genetic information carries 78 genes. Now if you can imagine pushing this little fellow from the top down, forcing it flat on a page of paper, you might get something like this:
The markers that have become recognized as distinct changes to tag for various genetic groups have been discovered. For the haplogroup R they are shown above. Each marker has a specific physical location along the genome. When this marker is found by DNA testing, it can identify a ethic group which has past on these changes. For haplogroup R, this change is believed to have occurred some 30,000 years ago, and has been labeled M173. The R1b marker is labeled M343, and the R1b1a2 marker is M269. It is interesting that the M269 marker is believed to have occurred some 5,000 to 8,000 years ago which is also the time that the English Channel was formed. At any rate, the following chart shows a big picture of the hapogroups as they have been thought to happen along the sands of time.
Note: The drawing above does not show the exact physical location along the genome of each mutation. It is drawn as an example. The "Gene Tree Haplgroups" I created for my own understanding some years in the past. Hopefully it will provide another way to visualize the chronology of this Y-chromosome.