I have some issues with IBD and IBS. Situation: Two full sisters tested, #2 and #3 One 1/2 sister tested #1 (all three same mother) Father of first two sisters tested #4. All four show a match to someone, Mister X :) In looking at the matching segments the 4 family members have with Mister X, it appears the girls' mother AND the father are related somehow to Mister X, but it also looks like Mister X is related to this group on two different lines, one thru the mother and the 3 daughters, and one thru the father and the two girls that are his daughters. For example the 3 girls match with Mister X on Chr 13: 1 @ 83339105 - 98287751, 15.88,4200 2 @ 83339105 - 94106590, 8.41, 2500 3 @ 83339105 - 99677030, 17.17, 4600 OK, I'm pretty sure then the above 'match' is through the mother of all three, since the father of the two doesn't show a match at this area of Chr 13, and #1 above is not the child of the father of #2 and #3. Then there is a section of Chr 12 where #2 and #3 (full sisters) and their father, #4, have a match with Mister X: #2 @ 72127478 - 76510591, 4.23, 1000 #3 @ 51411412 - 76510591, 25.09, 6200 #4 @ 51411412 - 76510591, 25.09, 6200 This looks to me like all three are connected to Mister X on the same line, even though #2 has a much smaller segment, but even if #2 isn't considered the same 'match' as #3 and #4, this shows a connection to Mister X thru the father of the girls. So those are large enough to be IBD. Scattered through out the other chromosomes are small sets of matching segments, most either with 1,2 and 3, or 2, 3 and 4. Normally I would think these are mainly IBS, but in this case where I have these specific 4 testers, and they share many of the smaller segments, isn't there a good chance many/most of these smaller 'matches' are also IBD? There are several combinations of the 4 matching Mister X, but no match ever includes #1 and #4 together. One example of a small matching segment, Chr 6: #1 @ 129879242 - 132216752, 3.15, 700 #3 @ 129879242 - 132216752, 3.15, 700 Since #1 and #3 share the same mother but not the same father, this would come from the mother's side, so are these small matching segments more likely to be IBS or IBD? melissa springer robards