Question

Is there a way to determine the cM of a segment from start and end positions of a segment?

Comments

PS-you might get more expert answers than mine if you tag your question with a dna tag in that field at the bottom of the question box

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Thanks for the tip!

Answer 1

Hi Kent! 

I think one answer is 'not without some other information as well'.

See the info here: https://isogg.org/wiki/CentiMorgan

Cheers

Shirlea

Answer 2

Yes. That's what the big companies do anyway. If you have a look at this paper:

https://www.researchgate.net/publication/7669813_A_map_of_the_human_genome_in_linkage_disequilibrium_units

It contains the map for one chromosome (19). There is somewhere a paper with maps for all human chromosomes, but I can't find the link at the moment. They all follow the same basic shape. You're more likely to get a recombination event at the start and end of any chromosome than in the middle, and the shape of the curve is always different for men vs women.

There is an online tool that's meant to do the sums for you, but it seems to be broken at the moment:

http://compgen.rutgers.edu/map_interpolator.shtml

You can download the raw data to generate the graphs yourself from the same website - but not for the faint of heart, it's a lot of data.

Comments

I used to use the Rutgers tool, too, but I think they may not be maintaining it anymore. Their graphs are still available in the WayBack Machine

http://web.archive.org/web/20070113005025/http://compgen.rutgers.edu/maps/compare.pdf

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Thanks Ann, that's the link I couldn't find.

Answer 3

There is a free utility program for conversion of base positions to cM. It will also convert between Build 36 and Build 37. I haven't checked lately, but I think FTDNA is still using B36 for segment boundaries. 

https://www.maps-phasing.com/

Chrome and Firefox flag the file as potentially dangerous simply because it's not commonly downloaded. They change the file name, and you will need to rename it so it ends in .exe in order to install it. I have corresponded with the author Hendrik Wendlund, and I can vouch for him. He also has a utility for phasing files, which is not free.

Answer 4

It should be possible to approximate at least reasonably closely.  See my answer and Edison's commentary at https://www.wikitree.com/g2g/539385/computing-cm-for-triangulated-segment.  Adjust the Build based on your test.