Inconsistent Ancestry Results #dna

Herbert Lazerow

Greetings, all. Here is something I don't understand. Ancestry shows a young
relative whose great-great grandmother was an elder sister to my
grandfather. She is a "very high match" (49 centimorgans shared across 7 DNA
segments) whereas her own sister shows as an "extremely high match" (72
centimorgans shared across 8 DNA segments).>
Those are only high matches for 4th cousins or more distant
relations. 49/7 means that the longest string is at least 7
centiMorgans long, probably a bit longer. 72/8 means that the longest
string is at least 9. None of those indicates a closer relationship
than 4th cousins, and the 72/8 sibling is more likely to be a 4th
cousin than the 49/7.
I am stumped why two siblings
would not have the same match numbers.>
They are likely to have similar match numbers to their parents
because we each receive roughly 50% of our dna >from each parent. They
are unlikely to have similar match numbers with other relatives
because the 50% we receive >from each parent is a random 50%. So each
sibling may have received the same percentage of dna >from each parent,
but unless they are identical twins, it will be a different mixture of
each parent's genes.
Illustration: Assume siblings of the same parents. S1 receives
genes A-D >from dad and E-H >from mom. S2 receives genes A-B and E-F
from dad, and genes C-D and G-H >from mom. They share only genes A-B
from dad and genes G-H >from mom.
S1 has a son GS1 who receives 50% of S1's genes. GS1 receives
genes A-B (dad's genes) and F-G (mom's genes) >from S1. GS1's other
genes (C, D, E & H) come >from S1's marriage partner. S2 has a son
GS2. GS2 receives genes A (dad's gene) C (mom's gene), F (dad's gene)
and H (mom's gene) >from S2. GS2's other genes (B, D, E & G) come from
S2's marriage partner. Note that only gene A matches between GS1 and
GS2 because it came in both cases >from dad. Each GS continues to carry
some of mom's genes and other genes >from dad, but the genes GS1
carries >from mom do not match the genes that GS2 carries >from mom, nor
do the other genes each inherited >from dad.
Herbert Lazerow
San Diego CA 92110

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