Did you know “Y-chromosomal Adam” is the ancient father of all people living today?
Tracing the SNP variation in your Y-DNA
Differences in the outward physical features of people from around the world make us appear very uniquely distinct from each other. However, our DNA, the hereditary material that carries information on how to build a human being, tells quite a different story. If you compare the DNA between two people from different parts of the world, 99.5% of the genetic code is identical. Just as the ‘out of Africa’ theory predicts, DNA studies have shown that all modern humans originated from a single population of people in Africa over 100,000 years ago, and eventually spread around the world.
As humans migrated around the world, they had to adapt to differences in climate, lifestyles and natural disasters. Many of these adaptive changes were possible due to random beneficial changes in our DNA. Randomly occurring genetic changes also enable us to trace our ancient origins, and to reconstruct the genetic family tree of mankind. Using differences in our DNA, geneticists have even identified the genetic mother and father of all modern humans. These genetic “parents” lived over 100,000 years ago, and are nicknamed “Mitochondrial Eve” and “Y-chromosomal Adam”.
Single nucleotide polymorphisms (SNPs) are the type of genetic marker that was used to find both “Mitochondrial Eve” and “Y-chromosomal Adam”. Nucleotides are the building blocks of DNA throughout our genome. A SNP is a change at just a single nucleotide. SNP markers have a very slow mutation rate, making them useful for tracking genetic changes that happened more than 1,000 years ago. Another genetic marker, known as a short tandem repeat (STR), has a much faster mutation rate, so is useful for tracing more recent ancestry.
SNPs and STRs occur throughout the genome – in all the autosomal chromosomes, and the X and Y sex chromosomes. Females have two X chromosomes, one inherited from each parent. Males have one X chromosome (inherited from their mother) and one Y chromosome (inherited from their father). Hence, paternal ancestry is traced by SNP and STR markers found in just the paternally-inherited Y chromosome. These markers are passed down unchanged from father to son, and can be used to trace patrilineal ancestry all the way back to the genetic forefather of all modern men – “Y-chromosomal Adam”. Maternal ancestry can also be traced, but this is through a different analysis of mitochondrial DNA.
The first tree for the Y chromosome was made in 2002 by the Y Chromosome Consortium, a group of scientists interested in mapping the evolutionary history of the Y chromosome. An evolutionary tree is like a family tree, and shows all of the different families that arise from a single person. Using genetic data from the Y-DNA analyses, scientists have generated a patrilineal ancestry of all modern men with “Y-chromosomal Adam” at the root of the tree.
The major branches of the tree are called haplogroups identified by letters (A to T). Haplogroups can be thought of as ancient family groups that existed thousands of years ago. These family groups were defined based on Y-DNA SNP profiles. Most haplogroups have a geographical location of origin. For example, haplogroup A is largely restricted to Africa, whereas haplogroup F may have originated in South Asia. Haplogroups can be further divided into finer sub-branches known as subclades.
Finding out your Y-DNA haplogroup allows you to retrace the steps of your ancient paternal ancestors, and take a journey back through time. A Y-DNA STR analysis is the first step in the determining your Y-DNA haplogroup. Often this Y-DNA STR is all that is required to accurately determine your haplogroup. Y-DNA STR analyses also have the benefit of providing data on more recent ancestors, and might even show that you are related to a famous person! Additional analyses of Y-DNA SNPs can also be conducted to confirm your haplogroup and determine which subclade you belong to. As more Y-DNA sequences become available, the Y chromosome tree keeps expanding, and maybe scientists will one day be able to tell the entire story of our ancient origins.