1. % Shared DNA (expectations)
Parents always give 50% of their genes to their offspring. Other relationships would be reduced by ½ for half-siblings, half-aunts/uncles, etc.
Remember that these values are actually a range (not a single value)
This graphic assumes that relatives share two common ancestors.
How would expectations change if there were only one common ancestor?

2. Kinship - Coancestry vs Covariance
Dad (Sire)
Mom (Dam)
From Grandpa
From Grandma
100 cM X
Shared chromosome segments
Child #1
In Plant Breeding – the female is always listed first (not so in human genealogy). Full IBD = 25 cM, ½ IBD = 50 cM, full + half = 75 cM
Child #2
What % of the DNA is expected to be shared between the two children? (this is covariance)
What would be the expected level of inbreeding in an offspring of Child #1 and Child #2? (this would be equal to their coancestry)
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?

3. Full-sib Covariance 25 25 25 A1A2 X A3A4 Expectations Half-IBD 50 cM
Shared chromosome segments 25 25 25
A1A2 X
A3A4
100 cM
Expectations
Half-IBD 50 cM
Full-IBD 25 cM
At least one match 75 cM
No Match 25 cM
Chance of no shared alleles?
Child #2
A1A3
A1A4
A2A3
A2A4
1/16
Child #1