Question

can i assume that a match on chromo 9 (29 cm) and chrom 23 (24 cm) are on the same 4th gen as given by gedmatch?

Answer 1

You need to tie the match in to the paper trail. You cannot just assume that the generational calculation given by gedmatch is correct. It is a good starting point for further investigation.

Not clear what you mean by listing the two chromosomes in your question. Are these for the same match?

Comments

Thanks Lynda. i can assume that the 4.6 gen is  for chromo 9 a distant ancestor different from the one on chromo 23

but gedmatch doesn t give  for the chromo 23 the x  the possible generation! coud you explain me why?

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You need to do one-to-one comparisons on Gedmatch to see where a pair of people match. And to triangulate, you need to use the one-to-one feature to determine that all  three people match with each other on the same segment.

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Thanks Ellen

now can someone explain why gedmatch doesn t give the n generation

for a match on the chromo 23

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Short answer is that X chromosome inheritance doesn't work the same way as inheritance of other chromosomes.

See the DNA Ancestors feature under Family Tree and Tools for information on the average percentage of X DNA you could have gotten from various ancestors.

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i think we can find triangulation on chromo 23  but they are farther  : am i correct!

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Yes, we can triangulate with chromosome 23, and good matches can exist farther back than with other autosomal chromosomes, but the potential for a good match varies depending on which ancestral branch you are related on.

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Thanks Ellen

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The big advantage of a match on the X-chromosome is that you can use it to narrow down which lines have potential common ancestors. You can eliminate any line that passes through two consecutive males.

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Thanks again but i knew it!

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The Wikitree DNA Ancestors page is a great feature. It shows which ancestors could be the source of X chromosome DNA and how much each would contribute (on average).