Photo courtesy of Tim Janzen
Let’s explore autosomal DNA in greater depth. As mentioned in my previous blog, the majority of our DNA is autosomal DNA. This DNA is found in 44 of our 46 chromosomes. Autosomal DNA is highly useful for genealogical purposes. As a general rule, the more autosomal DNA that you share in common with another person, the more closely related you are to that person. A child receives 50% of their autosomal DNA from each of their parents, and similarly on average a child receives a 25% contribution to their DNA from each of their four grandparents. So it goes as you go back through each generation until you reach a point about six to seven generations back where there is no guarantee that you will inherit a segment of DNA from each ancestor in your family tree at that level, due to the random nature in which individual blocks of autosomal DNA are passed down from parent to child.
It is also important to have some understanding about the percentage of autosomal DNA that siblings, first cousins, and other more-closely related relatives share in common with one other. Generally speaking, siblings share 50% of their DNA, and first cousins share about 12.5% of their DNA, on average. However, these percentages can vary somewhat widely with some siblings sharing 60% or more of their DNA in common, while other siblings only share 40% or less. Similarly, first cousins can share as little as 7% of their autosomal DNA or as much as 15%. For more detail about the ranges and averages that are involved for each level of relationship, I would suggest you consult my reference charts.
The exciting thing about autosomal DNA testing for genealogical purposes is that this type of testing can identify cousins that you have not previously known about. Many of these cousins are distantly related to you, but some may be closely related. If you carefully study the pedigree charts of your genetic cousins, in some cases you can identify surnames or ancestors that you share in common with these matches. If you can identify specific DNA segments that you share in common with two or more people, then careful review of those people’s pedigree charts can potentially help you identify shared surnames that can help you break through genealogical brick walls.
There are currently three primary genetic genealogy companies that offer autosomal DNA testing for genealogical purposes: 23andMe, Family Tree DNA (FTDNA), and Ancestry.com. The tests offered by these companies are similar in that they all use “SNP chips” that test between 700,000 and 967,000 specific point mutations called SNPs (single nucleotide polymorphisms). 23andMe’s test includes the most SNPs in its test.
If you are interested in receiving a consultation with Dr. Janzen, please contact Record Click for more information.