Tracing Your Ancestors Using DNA by Graham S Holton

Author:Graham S Holton
Language: eng
Format: epub
Tags: HISTORY/General
ISBN: 9781526733108
Publisher: Pen and Sword
Published: 2019-06-29T16:00:00+00:00

Figure 4: Advice from YSEQ.com on which new variants may be unsuitable for analysis via single SNP testing. https://tinyurl.com/yavr8msl.

Exploring and mapping the Y sequence

So, having taken this extended expedition through the wild geography of the Y chromosome, we can move on to look at how it is sequenced. One last point – there is a mapping reference system for all chromosomes, which starts at the left side of the diagram and numbers each locus on the chromosome in order until we reach the right side. The Y has approximately 58 million loci, varying slightly from build to build. The ‘readable Y’ falls roughly in the range 2,780,000 to 26,000,000, with the heterochromatin stretching beyond that for 30,000,000 loci (or possibly more, as it is not possible to exactly determine its length, and it may be highly variable in different men). The locus number can be used as a coordinate in much the same way as coordinates on a map.

A very useful resource for Y test-takers is YBrowse, which was created for and supported by ISOGG – try it at http://ybrowse.org/. If you want to look up the location of a Y-SNP, you can enter its name in the search box. You can also enter a locus to see whether there is a known SNP at that site. The Y coordinate needs to be entered in a particular way – try entering this locus, and use the format as shown here:

chrY:20577481..20577481

You have just entered the hg38 coordinate for M269, one of the most widespread SNPs among European-descended people. If you are a man in the widespread haplogroup R1b, you are very likely to be positive for this ancient SNP. Now try entering the following into the search box: L91. This is a defining SNP in the G haplogroup, and was found in the Y chromosome of Ötzi ‘the Iceman’, an ancient European found mummified in the Tyrolean Alps in 1991. If you have this SNP on your Y, you will be a (very distant) relative of Ötzi. You should see something like Figure 5, and you can notice that L91 has alternative labels (PF3246 or S285): a common problem, as many labs like to name the SNPs they find, and many of them have been found more than once. The additional label rs755612010 is the reference code for this SNP in the academic database of SNPs, dbSNP (not generally used in genetic genealogy).

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