When you go to the autosomal DNA statistic chart on ISOGG, roughly these are the estimated percentages of DNA/total cM's you should share.
25% 1700 cM (grandparents, aunts, uncles, double first cousins, half siblings)
12.5% 850 cM (great grandparents, first cousins, half niece and nephew, great uncles/aunts, half aunt/uncles, child of double first cousin (2nd))
6.25% 425 cM (first cousin once removed, half first cousin, grandchild of (double first))
3.125% 212 cM (first twice removed, second cousin, great grandchild of (double first)
1.563% 106.25 cM (second once removed, half second cousin)
.781% 53.13 cM (third cousins, second cousin twice removed)
.391% 26.56 cM (third cousin once removed)
0.195% 13.28 cM (fourth cousin, third cousin twice removed)
3.32 cM fifth cousin
0.83 cM 6th cousin
My parents results however when compared to known genealogical relationships is however, nothing like this.
My mother's results
Estimated 1st Cousin 850 cM (25 percent) (None)
Estimated 2nd cousin 290-350 cM (None)
2nd cousin once removed 152 cM
3rd cousin 98 cm – 145 cM
2nd cousin twice removed 46 cM (two both)
3rd cousin once removed 65-74 cM
fourth cousin 39-49 cM
5th cousin 28 cM
6th cousin 22 cM-42 cM (most likely estimate 11-17 cM)
Her second cousin once removed and one of her second cousin twice removed come from siblings of her grandmother, Elizabeth Ruth Timmins. The other second cousin twice removed comes from a sibling of her grandfather Leroy Hinds, and the two sixth cousin matches come from the Corliss line which is associated with the family.
Two of the third cousins, and one of the third cousin once removed are from the sibling of John Hager, mom's great grandfather. The other third cousin, a fourth cousin, a third cousin once removed and a 5th cousin are from the Rogers family. The final 3rd cousin once removed has proven to be a particularly challenging case. He matches a single 74 cM segment with my mother, and his relationship is estimated as he is adopted. The back half of the segment matches the Rogers family but none of the individuals matching the front half match the back. She has also matched a fourth cousin to her great great grandmother, Martha Collins.
Aside from the Corliss/Hinds family which was early colonial and can have higher percentages, the rest have no known consanguinity soI can't explain the consistency in the results for such higher percentages of DNA shared.
My father's results
Estimated 1st cousin 850 cM (none)
Estimated 2nd cousin 379 cM
** Note this is suspected to descend from a double first cousin..so it could be a second cousin once removed (double first shares 25 percent... second from this 12.5, once removed 6.25%)
2nd cousin twice removed 76 cM
3rd cousin 42 cM
3rd cousin once 39 cM, 56.6 cM
4th cousin 13 cM, 42 cM, 49 cM, 60 cM and 100 cM (last is probably related twice)
My father's results seem to be all over the place, but the challenge here is that the majority of the relationships are to his McCurdy family. Two of these matches are actually McCurdy's twice, which will inflate the DNA shared. One of the fourth cousins shares so much, that I suspect the other side of her line, the Penton's is related to the Beck side of my father's line. One match estimated at a 2nd cousin has chosen to remain anonymous, however, based on some of the matches they share on gedmatch, I highly suspect that this individual is from my grandfather's double first cousin. Given the amount shared, it is most likely a grandchild or their child from one of this family, unless of course, he is just related to the individual along several lines and this isn't a true representation.
Recombination, and the exact amount of DNA passed along surely belies the table though, if my results are any indication. Though I must admit I have noticed a trend on the amount of DNA I have inherited from my parents.
When my parents have a match, about 75 percent of the time I will inherit the match. Depending on the number of segments, my inheritance is generally half of what they inherited, if they have 4 segments, I may get two, or if it is one segment, then I generally inherit the exact match. Thus, I think it is very probable that helps to explain why some of the matches seem larger than the expectation. If my mom shares 15 cM with an individual who is a 6th cousin, and I share the same 15 cM, obviously the formula doesn't work.
Though I want someday to figure out as many of the matches as I can, I am concentrating more on the larger matches, and the segments where so many individuals share them that the chance of figuring it out is much greater. Both my parents literally have 15-20 cM segments shared with a dozen people. I figure the odds are that between us all, sooner or later we can narrow it down to a location or a family.