Our human genome has been around a long time. Since its beginning, any random, permanent change in the DNA molecule has been called a "mutation". A change in one nucleotide base pair represents a "point mutation", and is referred to in genetic lingo as "single nucleotide polymorphism" or "SNP" which is pronounced "snip". The Y-chromosome is the smallest of those DNA chains called chromosomes, and is least likely to undergo mutations among all 46. [ that male stubbornness I guess] Once a single base pair mutates, it becomes a distinct marker for that chromosome. This marker is then past along among the male descendants. These markers have been identified, and have come to be called "haplogroups". They have been labeled using the alphabet A thru T, with "haplogroup A" starting things off. The following chart shows these haplogroups starting around 60,000 BC.
As time has progressed, these haplogroups have undergone additional genetic changes, at various additional sites, involving multiple nucleotide bases. [Whew...can you keep that straight] These are again random chances but involve at least two base combinations next to one another (tandem) or at different (variable) sites along the DNA molecule. These additional changes among the "haplogroups" are called "haplotypes". The number of haplotypes vary, and those haplogroups with the highest number of haplotypes are shown in the figure above.
Haplogroup "E" has the highest number of haplotypes with 58. This is followed by haplogroup "J" with 34, and haplogroup "O" with 31. My JONES surname haplogroup "R" comes in forth with 29 haplotypes.
Now if you take the number of haplogroups and divide by the number of "1000 year of existence", you come up with a ratio of mutations per thousand years! For example, if you take haplogroup "E" with its 58 haplotypes and divide by 50 [ the number 50,000/1000 = 50] you get a ratio of 1.16 mutations per 1000 years. If you take my JONES haplogroup "R" [29 divided by 30,000/1000 ] you get a ratio of .967 per 1000 years. However, if you take haplogroup "J" [ 34 divided by 25,000/1000] you get a ration of 1.36 mutations per 1000 years. How about that...you get roughly 1 mutation per 1000 years for the haplogroups. Haplogroups to haplotypes...part of our human family tree.
Data taken from "Y-Chromosome Phylogenetic Tree" from Genome Research and Family Tree DNA.