% Shared DNA (expectations)
This graphic assumes that relatives share two common ancestors.
How would expectations change if there were only one common ancestor?
www.isogg.org/wiki/Autosomal_DNA_statistics
Kinship - Coancestry vs Covariance
Dad (Sire)
Mom (Dam)
From Grandpa
X
From Grandma
100 cM
Shared chromosome segments
Child #1
Child #2
1. What % of the DNA is expected to be shared between the two children? (this is covariance)
2. What would be the expected level of inbreeding in an offspring of Child #1 and Child #2?
(this would be equal to their coancestry)
3. If both children are DNA tested (they are humans now), how many cM are expected to be
IBD on both chromosomes (full-IBD)? On just one chromosome (half-IBD)? If the test does
not distinguish full and half IBD, what is the total cM that are expected to match?
Full-sib Covariance
Shared chromosome segments
A 1A 2
100 cM
Expectations
Half-IBD
50 cM
Full-IBD
25 cM
At least one match
75 cM
No Match
25 cM
X
A 3A 4
25
25
Chance of no shared alleles?
Child #2
A1A3 A1A4 A2A3 A2A4
Child #1 A1A3
1/16
A1A4
CovFS  
2
FS
   
1
2
2
A
25
1
4
2
D
A2A3
A2A4 1/16
1/16
1/16