Hi Dado, all,
?
It's not so much a mistake, but it is misleading. If you take an individual person to whom you are related and no mutations have occurred in your first 25 markers to separate you, then you are most likely related within the last 600 years, so a range of 1400 AD to 1950 AD is correct.
?
If we go back 250 years ago (about fifth cousins), about* 50% of your cousins should be exact matches to you. Go back about 600 years, and only about* 2.5% of your 15th cousins should be exact matches to you. (*Exact numbers will vary depending on the mutation rates you adopt.) However, you might find you have more matches to you 600 years ago than 250 years ago because 2.5% of your 15th cousins might be more people than 50% of your fifth cousins. And there are back mutations and convergent mutations on top of this.
?
I've tried to produce my own version of the table (this was going to go into the new version of the textbook, but it got axed), which I'll try to reproduce here. This is my estimate of the conversion between genetic distance and years before present. The ranges are 95% confidence intervals:
?
0/12 = 150 每 3600
1/12 = 260 每 4800
?
0/25 = 100 每 1560
1/25 = 160 每 2100
2/25 = 230 每 2800
?
0/37 = 60 每 840
1/37 = 110 每 1080
2/37 = 160 每 1380
3/37 = 200 每 1630
4/37 = 250 每 2000
?
0/67 = 40 每 680
1/67 = 80 每 800
2/67 = 120 每 970
3/67 = 160 每 1140
4/67 = 190 每 1340
5/67 = 240 每 1550
6/67 = 280 每 1750
7/67 = 320 每 2000
?
0/111 = 20 每 450
1/111 = 50 每 510
2/111 = 70 每 610
3/111 = 110 每 700
4/111 = 140 每 780
5/111 = 160 每 870
6/111 = 190 每 990
7/111 = 220 每 1080
8/111 = 240 每 1200
9/111 = 270 每 1300
10/111 = 290 每 1430
?
You can see from this how going to larger numbers of markers really starts to narrow down the ranges of how closely you are related to someone, but also how broad the possible range of dates is for the 12 and 25-marker datasets in particular. It's important to caveat this: this table is only true for the average person. If you have few mutations, common mutations or back mutations in your line, your ranges will be older; if you have many mutations, or rare mutations and few back mutations in your line, your ranges will be younger.
?
Since this is no longer going to go into the textbook, I'll try to write it up properly and post it on my website, but that may take me some time.
?
Cheers,
?
Iain.
