People have traditionally performed genealogical research by studying written documents. A new dimension has been added to genealogical research: the use of DNA. Each person has a "blueprint" in their body that contains information or instructions for the makeup and operation of their body. That blueprint is called DNA.
DNA is passed from parent to child in two ways. The Y-chromosome, that is passed from father to son, carries DNA information, and this information is referred to as Y-DNA. DNA information is also passed from mother to daughter and is known mtDNA. Y-DNA is used in genealogy because it is passed from father to son, and genealogical research is based on father-to-child relationships. Genealogists are beginning to use mtDNA, but its use isn't as widespread as that of Y-DNA.
Included in DNA is information about the origin of some of the person's ancestors. Humans are believed to have originated in Africa. The DNA of those ancient people was passed on to their children. However, occasional changes or mutations in DNA occurred, and the changes were also passed on to their descendants. As people spread over the earth, changes to DNA caused distinct patterns of DNA segments to appear. Today, those patterns are called haplogroups, and they give a general idea where particular genealogical lines came from tens of thousands of years ago.
The following chart shows how various Y-DNA haplogroups have separated from the original haplogroup that was in Africa, and the chart shows that haplogroups are a convenient way of identifying different genealogical lines. For example, many of the Leigh/Lee lines in the United Kingdom are of haplogroup RB1. Some of the Leigh/Lee lines in the UK, though, are of haplogroup I. The chart shows that the RB1 and I haplogroups originated from different people in different parts of the world, and this leads to the conclusion that the Leigh/Lee lines of haplogroup I are not related in a genealogical time frame to the Leigh/Lee lines of haplogroup RB1. Of course, haplogroup I is a large group of people, and not all of the Leigh/Lee lines in that haplogroup are related to each other.
Click the picture for a larger view of the chart.
This site focuses on the genealogy of people of haplogroup I. The ancient people who became haplogroup I migrated towards Scandinavia. This migration spread the DNA of the migrants among local folks. Further spreading of the haplogroup I DNA occurred during the ice age by migrations from Scandinavia to the Balkans, southern France, Iberia (present day Spain and Portugal) and Italy. During the middle ages, the Vikings invaded a wide area in Europe for about 200 years and spread their DNA throughout that area. As a result, haplogroup I is found today in many countries in addition to the Scandinavian countries, but that haplogroup is not common in most countries outside of Scandinavia.