Karen I've tried to calculate this based on about 3380cM which we share with a parent (others with parent matches can post their experience). But at the 4th cousin level it's no feasible to divide two numbers to get a segment length, because a 4th cousin will likely show up with a segment on several chromosomes; and you have to consider that at each generation you and the match will "drift apart" in the amount shared. However, based on my experience so far one segment from a fourth cousin would be about 30cM. Perhaps the best way to learn this number is from examples of others. Jim - Sent from my iPhone - FaceTime! On May 16, 2012, at 5:07 AM, Karen Hodges <[email protected]> wrote: >>> Parents and 1st cousins - virtually 100 percent >>> 2nd cousins about 99 percent >>> 3rd cousins about 90 percent >>> 4th cousins about 50 percent >>> declining percentages beyond that >> > > Hi Ann > > Can you tell me what size segments are typical of a fourth cousin, 50% ? > > Karen > > > ______________________________ > For answers to Frequently Asked Questions about mailing lists, please see: > http://dgmweb.net/MailingListFAQs.html > > > ------------------------------- > To unsubscribe from the list, please send an email to [email protected] with the word 'unsubscribe' without the quotes in the subject and the body of the message

Thanks Jim. Karen > > I've tried to calculate this based on about 3380cM which we share with a > parent (others with parent matches can post their experience). But at the > 4th cousin level it's no feasible to divide two numbers to get a segment > length, because a 4th cousin will likely show up with a segment on several > chromosomes; and you have to consider that at each generation you and the > match will "drift apart" in the amount shared. > > However, based on my experience so far one segment from a fourth cousin > would be about 30cM. Perhaps the best way to learn this number is from > examples of others. > > Jim - Sent from my iPhone - FaceTime! > >

Dear Jim, Karen, and others, In my database of comparisons the average number of shared cMs I have seen for 4th cousins who tested at 23andMe who come from non-endogamous populations is 10.7 cMs. This is from a total of 23 comparisons of known 4th cousins. The range for these comparisons is 0 to 30 cMs. If you include the matching segments between 4 and 5 cMs (only a portion of which are likely to be IBD), then the average increases to 19.9 cMs. In my 23 comparisons of 4th cousins at 23andMe, a total of 8 (34.8%) did not meet 23andMe's criteria for a match. Sincerely, Tim Janzen -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Jim Bartlett Sent: Wednesday, May 16, 2012 5:13 AM To: [email protected] Subject: Re: [AUTOSOMAL-DNA] Our atDNA matches are our cousins Karen I've tried to calculate this based on about 3380cM which we share with a parent (others with parent matches can post their experience). But at the 4th cousin level it's no feasible to divide two numbers to get a segment length, because a 4th cousin will likely show up with a segment on several chromosomes; and you have to consider that at each generation you and the match will "drift apart" in the amount shared. However, based on my experience so far one segment from a fourth cousin would be about 30cM. Perhaps the best way to learn this number is from examples of others. Jim -