Chromosome Mapping – Visualize Your DNA and Identify the Ancestors Who Passed It On To You
Have you ever tried to explain your pursuit of DNA matches, and found it hard put into words? Have you ever wanted to see an image of your DNA and how it connects you to your ancestors? Chromosome mapping will help you come up with an answer!
The goal in using DNA in our genealogy research is to learn which segments of our DNA we inherited from specific ancestors and use them to learn more about our parents, grandparents, and so on, back in time. Autosomal DNA is an extremely powerful tool that can help us confirm known ancestors and identify unknown ancestors. It can help us identify previously unknown relatives who may know more about our ancestors than we do. Newly identified DNA cousins may help us learn more about our shared ancestors or confirm speculated ancestors farther back in our shared ancestral line.
Chromosome mapping is an exciting technique that can be used to visualize your DNA and help you see the segments of DNA you inherited from your ancestors. Using your Autosomal DNA results, you can build a map of your chromosomes that shows segments that are inherited from specific ancestors or ancestral couples. Chromosome mapping is a more advanced technique you can use as you become increasingly familiar with DNA.
Some key concepts to keep in mind:
– You have 23 pairs of chromosomes in each of your cells; (or a total of 46 chromosomes). These chromosomes are numbered from 1 to 23.
– Autosomes are the pairs of chromosomes numbered 1 to 22. Autosomal chromosomes are similar in both males and females, and are numbered by size
– You receive 2 copies of each chromosome – one copy from your father and one copy from your mother
–The sex chromosomes are named X and Y; this is the 23rd pair of chromosomes
– Males inherit one X chromosome from their mothers and a Y chromosome from their fathers (XY)
– Females inherit two X chromosomes; one from their father, which was inherited from his mother, and one from their mother- which is likely a combination of X-DNA from her mother and father. (XX)
The following link will open a fantastic 2:07 minute video from Learn.Genetics that explains and illustrates principles of DNA inheritance:
Genetic Science Learning Center, “What is Inheritance?,” Learn.Genetics, 1 March 2016, ( https://learn.genetics.utah.edu/content/basics/inheritance : accessed 26 August 2019)
In the video, different colors represent segments of DNA that was passed down through the generations from the great-grandparents. Chromosome mapping will help you visualize the segments of your DNA you inherited from your great-grandparents and more distant ancestors.
1. Figure out how you and one of your DNA matches are related.
2. Identify the DNA segments you share with your DNA match–which sections of various chromosomes do you have in common with your relative?
3. Combine the information of how you are related, and the DNA you share with a match to determine which ancestors you share. These ancestors are likely the ones that passed that shared DNA on to both of you.
4. Next, you can label the DNA segments’ origin as you identify their locations on a chromosome map.
5. Continue using steps 1-4 to fill in your chromosome map. As time goes on, you will be able to use your personal chromosome map to help determine the common ancestors you share with unknown cousins identified in your DNA match lists.
6. Chromosome mapping can be done on paper, or in computer programs. A newer program that has made chromosome mapping clearer and easier is DNA Painter.
(Image created by Suzanne Chesney and Robin Wirthlin)
Key concepts in genetic genealogy:
1. Identify the familial relationship.
2. Identify the DNA you share.
3. Use that information to identify your common ancestor
DNA Painter (www.dnapainter.com) is a fantastic, simple to use tool for chromosome mapping. DNA Painter uses only segment information, not raw DNA data, which ensures more privacy because people cannot see the exact sequence of nucleotides in your raw DNA data.
The site may be used for free, for one chromosome map, or a paid subscription will give the user access for advanced options and up to 50 chromosome maps. There are very clear instructions on the website, and you can get started quickly after reading through them.
1. Sign in by creating a username and password
2. Open a new profile
3. Click on Paint A New Match
4. Copy the whole page of segment data from 23andMe, FTDNA, MyHeritage or Gedmatch
5. Paste the whole page into the Paint A New Match box
6. Answer the prompted questions, including if you know – or don’t yet know -how you are related to the match, and if the match is on your paternal or maternal side
7. Assign a color to an ancestor or ancestral couple that is the common ancestor between you and your DNA match.
This graphic is a chromosome map made in DNA Painter. The chromosomes are arranged from 1 at the top to 22, and X at the bottom. There are two lines for each chromosome, the top line represents the paternal copy and the bottom line represents the maternal copy. The colored lines are segments of DNA that have been mapped to a certain ancestral couple. The DNA was identified as coming from each couple because it was shared with a DNA match that has the same common ancestor as the DNA test taker.
A challenge you may encounter in mapping your chromosomes is that you may have multiple common ancestors with your DNA matches. If this is the case, you will share more DNA than expected with the DNA match, and it may be more difficult to identify which DNA segments came from a specific ancestor or ancestral couple. Some of the situations you may encounter are the following:
Family tree completeness:
– You may not know if you share multiple ancestors with a DNA match if you have some ancestral lines that are shorter because some ancestors aren’t identified- AKA: dead ends or brick walls.
You may share multiple common ancestors with a cousin:
– If there is pedigree collapse – this happens when related individuals have children. These children have fewer unique ancestors than expected because their parents have some ancestors in common.
– If there is endogamy – this occurs among some populations who are geographically isolated, or populations who choose to primarily marry within the population, and the children inherit DNA that is descended from the founders of the population in multiple ways.
Another type of Chromosome map is Visual Phasing. It is a method that can be used to determine which segments of your DNA came from your four grandparents; two maternal grandparents and two paternal grandparents. Visual Phasing is a more time-intensive way to map your chromosomes. The benefit of this method is that you will be able to create a detailed map that identifies DNA segments from each of your 4 grandparents.
Blaine Bettinger wrote a 5-part series of instructions on how to do Visual Phasing. https://thegeneticgenealogist.com/2016/11/21/visual-phasing-an-example-part-1-of-5/ Some of the starting requirements are that you need a set of 3 siblings, determination, focus, and patience. The goal is to map crossover points in your chromosomes. These are points on the chromosome where DNA from your grandparents has switched places or recombined.
Steven Fox wrote a program in Excel that helps automate the process of Visual Phasing. The program can be found in the “Visual Phasing Working Group” on Facebook. https://www.facebook.com/groups/visualphasing/
Chromosome Mapping using DNA Painter and Visual Phasing techniques can help further your DNA and genealogy research. Chromosome mapping can help you find out more about your DNA and the ancestors who passed it on to you. Try these tools as you Research Like a Pro with DNA!