Shared Chromosomes -Part 2 The Family

In this part of the series I will show how a family of DNA testers can collectively give guidance as to which side of the family a match emanates.

 
A friend and member of one of the projects I administer was kind enough to allow me to use his family for this study. I will not use any of their names but will call them Son, Mother, Father and Grandmother. The Grandmother is the mother of the Father.

 
The Son and Father share 3384.30 cM    (cM is centi-Morgan, the term used in DNA for length) with the longest block 267.21 cM

 
The Son and Mother share 3383.73 cM with the longest block 267.21 cM

The Son and Mother share an X-Chromosome.

 
The Son and Grandmother share 1361.17 with the longest block 176.25 cM

 

The Father and his own mother, the Grandmother share 3383.30 cM with the longest block 267.21 cM. They also share an X-Chromosome.
Since males do not inherit X-Chromosomes from their fathers, the Son inherited an X-Chromosome from his mother but not his father’s mother, the Grandmother.
Note above that the Son inherited his genomes virtually equally from each of his parents. This is the only time in any generation of the Son’s pedigree where he will inherit equally from two ancestors. In subsequent generations, including his Grandparents, he will inherit approximate amounts. From one Grandparent or Great Grandparent he will inherit one amount and more or maybe less than the that Grandparents partner.

 
Children inherit almost exactly 50% of their DNA from each of their parents. However, they inherit approximately 25% from each of their four Grandparents. From one Grandparent they may inherit percentages more or percentages less than 25%. Notice below, the Son inherited 1361 cM from the Grandmother. Had he inherited 50% of his Grandmother’s DNA from his Father, he would have inherited about 1642 cM rather than the 1361cM he did inherit.

 

 

The Family’s Shared Chromosomes

 
The Son has 65 pages of matches totaling 648 matches

 
The Father has 28 Pages in common with the Son totaling 276 matches

 
Likewise, the Father has 38 Pages NOT in common with the Son totaling 371 matches

 
The Mother has 24 Pages in common with the Son totaling 240 matches

 
Likewise, the Mother has 41 Pages NOT in common with the Son totaling 407 matches

 
The Grandmother has 13 Pages in common with the Son totaling 128 matches

 
Likewise, the Grandmother has 52 Pages NOT in common with the Son totaling 519 matches

 
The Father and his mother, the Grandmother, share 30 Pages in common with one another totaling 300 matches

 
Likewise, the Father and Grandmother share 30 Pages of NOT in common with one another totaling 300 matches.

 
In Summary-How It Works

 
So, what do all these matches “in common with” and “NOT in common with” mean?

 
When the Son has a cousin match and the Father also matches the same cousin, the relationship is on the Father’s side of the family. If the Son has a cousin match and the Father is not a match, then the relationship is on the Mother’s side.

 
It is exactly the same scenario when the Son has a cousin match and the Mother also matches the cousin. The cousin is related on the Mother’s side. Likewise, if the Son has a cousin match and the Mother does not match, the relationship is on the Father’s side.

 
It is also fortunate for the Son that he has his Grandmother. If the Son or the Father has a cousin match and that cousin also matches the Grandmother. The relationship is on the Grandmother’s side.

 
If the Son and the Father match the cousin and the Grandmother does not, then the relationship is on the Grandmother’s husband’s side, the Grandfather.

 
Below is a Chromosome Browser illustration of this simplistic Son, Father, Mother, Grandmother family.

 
The Chromosome silhouettes belong to the Son.

 

The lines superimposed on the chromosomes represent the relatives matching him.

 

The first line (Gold) is the Father, the second line (Tourquoise) is the Mother and the third line (Green) is the Grandmother. Notice how all of each chromosome is covered by the Father and Mother and only part is covered by the Grandmother.

 
Also, notice the X-Chromosome shared between the Son and his Mother on Chromosome 23

 
Sorry, the browser is broken in two parts- Chromosomes 1-13 and 14-23. On the actual Browser all chromosomes are connected 1-23. The chromosomes in the Browser on this page had to be broken in two to get all chromosomes in the picture.

 
On the Son’s Match Page, the second set of two Browser parts showing Chromosomes 1-13 and 14-23 illustrate the Father (Gold) and his Mother, the Grandmother (Tourqouise) . The Father is the first line and the Grandmother is the second line. Notice the Father shares his mother, the Grandmother’s X-Chromosome on Chromosome 23.

 
Line 1 Father-Gold
Line 2 Mother-Tourqouise
Line 3 Grandmother-Green

Line 1 Father-Gold
Line 2 Grandmother-Tourqouise

 

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