Charts for Understanding DNA Inheritance
When using DNA test results as evidence in genealogy, it’s important to understand contextual information about DNA inheritance patterns and amounts of DNA shared between relatives. This contextual information can turn raw DNA data into genealogical evidence. In this post I will share several charts that give meaning to the data in our DNA test results. The charts I’m sharing are freely available online. Another excellent source for inheritance charts is the book Genetic Genealogy in Practice by Blaine T. Bettinger and Debbie Parker Wayne. The charts in the book are well done and helpful for understanding the inheritance of autosomal DNA, mitochondrial DNA, and the X and Y-chromosomes.
mtDNA and Y-DNA Inheritance
Charles F. Kerchner has shared a helpful Y-DNA and mtDNA Inheritance Descendants Chart showing which descendants inherit Y-DNA and mt-DNA from a single common ancestor. You can view the chart here: Charles F. Kerchner, Jr. “Y-DNA and mtDNA Inheritance Descendants Charts,” 7 October 2007, Kerchner’s DNA Testing & Genetic Genealogy Info and Resources Page (http://www.kerchner.com/y&mtdnachart.htm : accessed 13 August 2019).
Autosomal DNA Inheritance
Several helpful diagrams and charts give meaning and context to your autosomal DNA test results. I’ve highlighted them below.
Average Percentages of Shared DNA
The following chart shows the average amount (in percentages) of autosomal DNA that is shared by close relatives. To read the chart, locate the orange box that says “self.” If you have taken an autosomal DNA test, you can expect to share about 50% of your DNA with your father/mother, brother/sister, and son/daughter. You can expect to share about 25% of your DNA with your granddaughter/son, grandfather/grandmother, uncle/aunt, and niece/nephew. This chart can help you understand the approximate amount of DNA inherited in each generation. It also helps visualize the concept of cousins and cousins removed, which is key when we’re working with autosomal DNA matches. To view the source of the chart go here: Dimario, “Cousin Tree (with genetic kinship),” Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Cousin_tree_(with_genetic_kinship).png : last updated 27 April 2010).
Genetic Family Tree vs. Genealogical Family Tree
Blaine Bettinger, “DNA Solutions: Genealogical vs. Genetic Family Trees,” May 18, 2016, Family Tree Magazine (https://www.familytreemagazine.com/index.html%3Fp=7832.html : accessed 13 August 2019).
Blaine Bettinger, “Q&A: Everyone Has Two Family Trees – A Genealogical Tree and a Genetic Tree,” 10 November 2009, The Genetic Genealogist (https://thegeneticgenealogist.com/2009/11/10/qa-everyone-has-two-family-trees-a-genealogical-tree-and-a-genetic-tree/ : accessed 13 August 2019).
X-Chromosome Inheritance Charts
If you find that you are an X-match with someone, you can use the unique X inheritance pattern illustrated in the following charts to narrow the possible common ancestors. Blaine Bettinger created two X-DNA inheritance fan charts, one showing who a female may have inherited her X-DNA from, and one showing the same for a male. The pink ancestors are females who may have contributed X-DNA, and the blue ancestors are males who may have contributed X-DNA. View the charts here: Blaine Bettinger, “Unlocking the Genealogical Secrets of the X Chromosome,” 21 December 2008, The Genetic Genealogist (https://thegeneticgenealogist.com/2008/12/21/unlocking-the-genealogical-secrets-of-the-x-chromosome/ : accessed 13 August 2019).
The Shared cM Project Tool
To use the Shared cM Project Tool, go here: Blaine Bettinger and Jonny Perl, “The Shared cM Project 3.0 tool v4,” DNA Painter (https://dnapainter.com/tools/sharedcmv4 : accessed 13 August 2019).
Autosomal DNA Statistics
A chart contained in the article “Cousin Statistics” on the ISOGG Wiki details the probability that two cousins will share enough DNA for the relationship to be detected. Each testing company reports different probabilities. The chart includes data from 23andMe, AncestryDNA, and Family Tree DNA Family Finder. The article also includes charts with theoretical probabilities and estimates about the number of cousins we have. View the article and charts here: “Cousin Statistics,” The International Society of Genetic Genealogy Wiki (https://isogg.org/wiki/Cousin_statistics : last modified on 20 September 2017, at 13:21.)
To view my Pinterest board with these charts and others pinned, go here: DNA Inheritance Charts for Genetic Genealogy.