What's important to do now is to fill in the MRCA-C column that is shown above by the red box. This column contains the Most Recent Common Ancestor (MRCA) between A and C expressed from A's point of view up to the ancestor. There is a simple notation developed for you so that you can enter that information.
- Use "F" for the Father's line
- Use "M" for the Mother's line
- Use "R" to represent the paiR of ancestoRs who are the MRCAs.
For example. If person C is person A's 2nd cousin on their Father's Mother's side, then the MRCA should be entered as:
FMR
Here's some guidelines and you'll get the hang of it quick:
R - use for all descendants of Person A's parents. This includes Person A's children, grandchildren, siblings, nieces, nephews, great-nieces, etc.
FR - use for all descendants of Person A's father's parents. This includes Person A's father, aunts, uncles, 1st cousins, descendants of 1st cousins, etc.
MR - same as FR but on Person A's mother's side.
FFR - use for all descendants of Person A's father's father's parents. This includes Person A's grandfather, great-uncles/aunts, 2nd cousins, descendants of 2nd cousins, etc.
FMR, MFR, MMR - Same as for FFR except for father's mother's parents, mother's father's parents, and mother's mother's parents.
FMMMFFFFMMFMR - You can extend this to any level if you know your ancestry back that far.
But remember, we want the "Most Recent" common ancestral line which is the line that likely supplied most of the matching segments.
For half-relatives, e.g., half-siblings or half-uncles/aunts, go up to the level at which you share both ancestors, e.g.
FR - half sibling sharing father
FFR - half uncle/aunt sharing grandfather
Only enter MRCAs that you are fairly certain about.
If a person is equally related on through both parents, e.g. a first cousin of both your father and your mother, enter them as R. The MRCA overrules the cluster assignment and will prevent this person from influencing the ancestral path assigned to the segments.
Any person whose MRCA is assigned R and who shares from 2300 to 3300 cM will be assumed to be a sibling, and a line will be added into the log file for each sibling assumption. Siblings matches have to be handled by DMT in a custom manner because they match on both parents about 25% of the time. Currently, you cannot override DMT's assumption about siblings. If DMT is incorrectly assuming siblings, then remove the R from that person's MRCA or change it if it was wrong.
An R at the end of an MRCA indicates you know the MRCA exactly.
An MRCA without an R at the end, which is called a Partial MRCA, may be entered to indicate that you only know part of the line up to the MRCA, e.g.
MF - You know someone is on your mother's father's side but don't know after that (may be MFF... or MFM...)
Partial MRCAs not ending in R are a good way to enter partial lines that you might get from DNA clustering tools that use the Leeds Method or something similar.
Partial MRCAs will not overrule DMT's cluster assignment and DMT may extend or reduce or change the Partial MRCA when assigning the cluster to the person.
If a person is related more than one way, e.g., MFFR and MMMR, then you may enter a partial MRCA for them up to the point in common, e.g. in this example M.
Partial MRCAs are not used in inferrals, since inferrals need exact MRCAs.
DMT can only attempt to calculate ancestral lines as deep as the MRCAs you enter, so try to enter MRCAs for as many people on different ancestral lines that you know. However, avoid entering MRCAs that are very deep such as 6 or more generations unless you are certain that this person is not related through other ancestral lines.
Normally, you'll know most of the MRCA of your closer matches but fewer from your more distant matches. After you've entered your MRCAs, you should have something that looks like this:
As you enter the MRCAs, their background will get a shade that DMT associates with that parent or grandparent line. DMT adds conditional formats to these cells so that the shading will occur.
In the above screenshot, for example:
The two people sharing 3384 cM could either be parents or children. In this case, they are parents. The mother was given MR. The father was given FR. There are not any children here, but if there were, they should be assigned R. Since DMT makes special use of parent information, it is very important that the parents be given the correct MRCA. You should only have at most one person more than about 3300 cM assigned FR and at most one assigned MR. Unfortunately, many of us do not have the benefit of having one or both of our parents tested.
The person sharing 2709.9 cM is a sibling and is assigned R.
The people sharing 1711 cM and 1708.2 cM are both siblings of Person A's mother, so they are assigned MR.
The people sharing 307 cM to 483 cM are all 1C1Rs (1C of Person A's parent). There's a 2C1R sharing 66.5 cM.
The screenshot above only goes down to 51 cM, but don't forget to look through the people with lower match totals, as some may be known relatives who can be assigned an MRCA.
button.
and 
unchecked, and press the 
button.
button becomes activated. Press the button to open your People file.
