The pictures to the right and left are examples of sections DNA from the Y chromosome. We only use the first letter to indicate one of the 4 chemicals.
These pairs that make up the bonds of DNA are passed from parent to child through many generations without change, but very rarely, there will be a change in a single pair, as seen on the right.
This change is called an SNP and is very unlikely to occur again in any human except for the descendants of the man in which it originally occurred.
Tracing these SNPs lets us track our ancestors through thousands of years.
The SNP of the Hoy family is M222, but very recent work has refined that to new SNPs which are discussed on another page.