How many genetic ancestors do you have?

Short answer: you get DNA from about 2n ancestors n generations back, up to 8 generations, then about 68 additional ancestors for each generation after that.

Background

Other people have done this same analysis, see here and here. They got similar but slightly different results than I did.

The number of genealogical ancestors you have n generations is 2n: 2 parents, 4 grandparents, 8 great-grandparents, and so forth. The only way to have fewer is if some of them are the same person. (For example, I have two great-great-great-great grandparents who are also my great-great-great-great-great grandparents by another line.)

The difference between genealogical ancestors and genetic ancestors is that genetic ancestors are the ones that you actually got some DNA from. They're a subset of your genealogical ancestors. Humans have about 3 billion base-pairs of DNA, so that limits the number of genetic ancestors to about 3 billion no matter how far back you go. There are also around 46,000 hotspots (reference Genetic Crossovers Are Predicted Accurately by the Computed Human Recombination Map, figure 6). Hotspots are the places where crossovers usually happen. Each of the 46,000 segments bounded by neighboring hotspots usually has a single line of descent, so you're limited to about 46,000 ancestors.

But I'm interested in something that happens much sooner than that: after about eight generations back, the number of genetic ancestors only increases linearly with the number of generations, while the number of genealogical ancestors keeps increasing exponentially. Once you go back 20 generations, you have only 1300 or so genetic ancestors despite having over a million genealogical ancestors.

The exponential growth up to 8 generations is due to having many independent chromosome pairs. Humans have 23 pairs of chromosomes, and which side of the pair you inherit from is a random choice for each of the chromosomes. You start out with both sides of the pair yourself. For your parents, you got one side of each of the 23 pairs from each parent. Grandparents, that's about one side of 23/2=12 pairs. Great-grandparents, one side of 6 pairs each. Great-great-grandparents, one side of 3 pairs. Eventually you're down to inheriting DNA on just one side of one pair from each ancestor. At that point the exponential growth of ancestors stops.

The linear growth after that is a bit more complicated. The linear growth is due to having a limited number of crossovers per chromosome per generation. Each generation, you don't just get one side of one of your parent's chromosomes. Instead, the parent mixes their pair before splitting it into two. The process is called meiosis. The points where the pairs cross are called crossovers. There's around one or two crossovers per chromosome pair per generation.

Being more precise about crossovers (reference "Genetic Analysis of Variation in Human Meiotic Recombination"). The 23rd chromosome is special, it's the XY chromosome. If you're a male you have XY, if you're female you have XX. The male does not mix the XY, daughters get the X directly and sons get the Y directly. If you're female you have XX, and XX has about as many crossovers as any other chromosome. Other than that, there's always at least one crossover per chromosome per generation (otherwise meiosis doesn't work properly), and sometimes more than one. How many more is proportional to the length of the chromosome (reference Broad-Scale Recombination Patterns Underlying Proper Disjunction in Humans, figure 5). If you're male, you have an average of 26.4 crossovers total when producing sperm, so spread among 22 chromosomes, that's a little over 1 crossover per chromosome. If you're female, it's more like an average of 41.1 crossovers when producing eggs, so given 23 chromosomes total, that's a little under 2 crossovers per chromosome. Each generation each chromosome does these crossovers, and also decides randomly which side of each chromosome pair to give you.

If you're male, you got your Y chromosome from exactly 1 ancestor n generations back. The X chromosome (men have half a pair, women have a whole pair) is also unusual: you're most likely to get it from your mother's father's mother's father's mother etc, but it might have come from your mother's mother's etc. Reference That Unruly X ... Chromosome That Is.

Tables: number of genetic ancestors N generations back

So ... what's that add up to? How many genetic ancestors do you get n generations back? I simulated it, C++ code here, doing the crossovers at random spots, handling XY correctly, and the number of crossovers per generation for males and females correctly too. Other than XY, I treated all chromosomes as the same: same length, same chance of crossover. Instead of starting with 2n ancestors and trying to derive a person, I started with a person and worked backwards. Any ancestors contributing no DNA can be ignored, because their ancestors will also contribute no DNA, so the time and space complexity of the simulation is linear with the number of genetic ancestors for however many generations back you want to go.

Here's a table of the results, starting with a female:

# generations # genealogical ancestors minimum # genetic ancestors (10000 trials) average # genetic ancestors (10000 trials) maximum # genetic ancestors (10000 trials)
011 11
122 22
244 44
388 88
41616 1616
5323131.999132
6646163.846264
7128114123.973128
8256200220.158238
9512304342.472377
101024419470.809520
112048529590.278656
124096623696.141776
138192710789.701873
1416384784873.971966
1532768842951.9271047
16655369051026.051131
171310729661097.731206
1826214410411167.941273
1952428810961237.21343
20104857611701305.951429
21209715212431374.491504
22419430413091442.931578
23838860813711511.091653
241677721614411579.371722
253355443215061647.571795
266710886415791715.611868
2713421772816491783.771934
2826843545617191851.92009
2953687091217741920.12075
30107374182418451988.062141
31214748364819202056.222207
32429496729619862124.482284
33858993459220412192.532346
341717986918421092260.732416
353435973836821772328.92480
36687194767362243 23972557
3713743895347222962465.052621
3827487790694423542533.062689
3954975581388824292601.052768
40trillion24952669.142838
4124125702737.272901
4224226372805.462977
4324326952873.613064
4424427642941.743140
4524528403009.913210
4624629043078.063266
4724729693146.253336
4824830333214.343414
4924930973282.523481
50quadrillion31683350.773540
5125132373418.863609
5225233073486.963680
5325333663555.223750
5425434263623.33817
5525534933691.323893
5625635573759.333964
5725736263827.54030
5825836933895.654117
5925937613963.74172
60quintillion38154031.754239
6126138734099.864309
6226239304167.994379
6326339894236.174453
6426440594304.294531
6526541184372.534615
6626641834440.654688
6726742634508.924750
6826843334576.984836
6926944054645.114887
70sextillion44704713.324947
7127145304781.525016
7227245944849.665088
7327346494917.725158
7427447234985.735221
7527547875053.835297
7627648595121.965354
7727749315190.045428
7827849845258.165496
7927950575326.375573
80septillion51255394.435644
8128151865462.635715
8228252485530.865788
8328353195598.935856
8428453745667.015933
8528554555735.065991
8628655225803.286066
8728755925871.326148
8828856635939.436209
8928957316007.636277
90octillion58006075.86340
9129158526143.956407
9229259386212.166487
9329359926280.176573
9429460596348.326635
9529561336416.356699
9629661946484.446766
9729762626552.456831
9829863276620.466917
9929963886688.617001
100nonillion64446756.647076

And again, starting with a male:
# generations # genealogical ancestors minimum # genetic ancestors (10000 trials) average # genetic ancestors (10000 trials) maximum # genetic ancestors (10000 trials)
011 11
122 22
244 44
388 88
41616 1616
5323131.999532
6646063.84964
7128115123.852128
8256201219.26237
9512305340.044376
101024416466.124518
112048519583.348649
124096619687.065754
138192696778.726857
1416384774861.355955
1532768844937.9151031
16655369151010.51108
171310729721080.811185
1826214410381149.531255
1952428811131217.491332
20104857611821285.141399
21209715212411352.361474
22419430413031419.491540
23838860813621486.561609
241677721614341553.581676
253355443214941620.541759
266710886415441687.491833
2713421772816051754.431907
2826843545616661821.311976
2953687091217381888.222042
30107374182418031955.142114
31214748364818702022.082176
32429496729619262088.862243
33858993459219942155.772323
341717986918420592222.762388
353435973836821122289.612460
366871947673621802356.562514
3713743895347222342423.472582
3827487790694422992490.442652
3954975581388823662557.322732
40trillion24402624.22794
4124125022691.112859
4224225622757.972923
4324326152824.92998
4424426732891.873078
4524527412958.73157
4624628053025.653228
4724728593092.543287
4824829303159.453349
4924930013226.323419
50quadrillion30703293.223480
5125131543360.293548
5225232123427.343628
5325332733494.153695
5425433513560.963762
5525534173627.943822
5625634883694.863890
5725735583761.773968
5825836213828.654042
5925936933895.514108
60quintillion37543962.484172
6126138244029.434252
6226238854096.454325
6326339504163.374390
6426440114230.294468
6526540724297.164528
6626641444363.974608
6726741974430.844684
6826842654497.864753
6926943224564.874826
70sextillion43884631.814898
7127144494698.854966
7227245114765.775040
7327345824832.75107
7427446414899.515177
7527547094966.385242
7627647645033.215310
7727748265100.245378
7827848985167.245462
7927949645234.295533
80septillion50335301.185588
8128151105368.235655
8228251725435.175725
8328352335501.95781
8428452935568.695854
8528553535635.645915
8628654095702.55990
8728754725769.416070
8828855385836.366136
8928956065903.246200
90octillion56775970.156267
9129157336036.996339
9229257996103.846413
9329358796170.626488
9429459376237.546577
9529559966304.476647
9629660706371.336712
9729761466438.376773
9829861986505.346840
9929962726572.286912
100nonillion63416639.226966

Tables: number of genetic ancestors you got 2-n of your DNA from

One practical upshot of this is that those ancestors you do inherit something from, you inherit a lot from. And large stretches of DNA are passed down from generation to generation, those stretches usually aren't finely divided.

How closely related are cousins? It's pretty much a matter of the number of meioses again, except you go up to a pair of ancestors then down again. Siblings shared half their DNA due to inheriting from both parents. The same chart that shows how much DNA your ancestors contirbuted can show how much DNA cousins will shared, just about. There is the difference that the messiness around the common parents adds about one extra generation of splitting without adding one extra generation of diverging.

How many cousins do you have that share 2-X of your DNA? That cannot be answered by these charts directly: it is strongly influenced by how many children your ancestors had. If someone shared 2-X of your DNA, what type of cousin are they probably? Again can't tell, it depends on how many children your ancestors had. If they all had 2 children each, say for 2-9, you take the mean generation of the 9:??? values and that would tell you (somewhere between 2nd cousin and 100th cousin, with 7th cousin once removed most likely).

How many ancestors X generations back gave you closest to 2-Y of your DNA from (starting from a female):
generationnth cousinsY:Z, where Z ancestors gave closest to 2-Y of the DNA
00:1
1siblings1:2
22:4
31st cousins3:7, 4:1
43:1, 4:12, 5:2
52nd cousins4:5, 5:19, 6:7, 7:1
65:13, 6:30, 7:15, 8:4, 9:1
73rd cousins5:3, 6:29, 7:44, 8:27, 9:12, 10:5, 11:2, 12:1
86:14, 7:56, 8:64, 9:42, 10:22, 11:11, 12:6, 13:3, 14:1, 15:1
94th cousins6:5, 7:45, 8:91, 9:83, 10:55, 11:31, 12:16, 13:8, 14:4, 15:2, 16:1, 17:1
106:1, 7:30, 8:100, 9:123, 10:94, 11:57, 12:32, 13:17, 14:8, 15:4, 16:2, 17:1, 18:1
115th cousins7:19, 8:97, 9:152, 10:132, 11:87, 12:49, 13:26, 14:14, 15:7, 16:3, 17:2, 18:1
127:12, 8:89, 9:171, 10:166, 11:115, 12:68, 13:37, 14:19, 15:10, 16:5, 17:2, 18:1, 19:1
136th cousins7:8, 8:80, 9:183, 10:195, 11:142, 12:85, 13:47, 14:25, 15:12, 16:6, 17:3, 18:2, 19:1
147:5, 8:71, 9:190, 10:220, 11:167, 12:103, 13:57, 14:30, 15:15, 16:8, 17:4, 18:2, 19:1
157th cousins7:3, 8:63, 9:194, 10:242, 11:191, 12:120, 13:67, 14:36, 15:18, 16:9, 17:5, 18:2, 19:1, 20:1
167:2, 8:55, 9:195, 10:261, 11:214, 12:137, 13:77, 14:41, 15:21, 16:11, 17:5, 18:3, 19:1, 20:1
178th cousins7:2, 8:48, 9:194, 10:279, 11:237, 12:154, 13:88, 14:47, 15:24, 16:12, 17:6, 18:3, 19:2, 20:1
187:1, 8:42, 9:191, 10:294, 11:259, 12:172, 13:99, 14:53, 15:27, 16:14, 17:7, 18:4, 19:2, 20:1
199th cousins7:1, 8:37, 9:188, 10:309, 11:281, 12:190, 13:110, 14:60, 15:31, 16:16, 17:8, 18:4, 19:2, 20:1, 21:1
207:1, 8:32, 9:183, 10:321, 11:303, 12:208, 13:122, 14:66, 15:34, 16:18, 17:9, 18:4, 19:2, 20:1, 21:1
21108:28, 9:178, 10:333, 11:324, 12:227, 13:134, 14:73, 15:38, 16:19, 17:10, 18:5, 19:2, 20:1, 21:1
228:24, 9:172, 10:343, 11:346, 12:246, 13:147, 14:80, 15:42, 16:21, 17:11, 18:5, 19:3, 20:1, 21:1
23118:21, 9:166, 10:352, 11:367, 12:265, 13:160, 14:88, 15:46, 16:23, 17:12, 18:6, 19:3, 20:2, 21:1
248:18, 9:159, 10:359, 11:387, 12:285, 13:173, 14:96, 15:50, 16:26, 17:13, 18:7, 19:3, 20:2, 21:1
25128:15, 9:153, 10:366, 11:407, 12:305, 13:187, 14:104, 15:54, 16:28, 17:14, 18:7, 19:4, 20:2, 21:1
268:13, 9:146, 10:371, 11:427, 12:326, 13:201, 14:112, 15:59, 16:30, 17:15, 18:8, 19:4, 20:2, 21:1
27138:11, 9:139, 10:375, 11:446, 12:346, 13:216, 14:120, 15:64, 16:33, 17:17, 18:8, 19:4, 20:2, 21:1, 22:1
288:9, 9:132, 10:379, 11:465, 12:367, 13:231, 14:129, 15:68, 16:35, 17:18, 18:9, 19:5, 20:2, 21:1, 22:1
29148:8, 9:125, 10:381, 11:484, 12:388, 13:246, 14:139, 15:74, 16:38, 17:19, 18:10, 19:5, 20:2, 21:1, 22:1
308:7, 9:118, 10:382, 11:501, 12:409, 13:262, 14:148, 15:79, 16:41, 17:21, 18:10, 19:5, 20:3, 21:1, 22:1
31158:6, 9:112, 10:383, 11:519, 12:430, 13:278, 14:158, 15:84, 16:43, 17:22, 18:11, 19:6, 20:3, 21:1, 22:1
328:5, 9:105, 10:382, 11:535, 12:452, 13:294, 14:168, 15:90, 16:46, 17:24, 18:12, 19:6, 20:3, 21:1, 22:1
33168:4, 9:99, 10:382, 11:551, 12:473, 13:310, 14:178, 15:95, 16:49, 17:25, 18:13, 19:6, 20:3, 21:2, 22:1
348:4, 9:93, 10:380, 11:567, 12:495, 13:327, 14:188, 15:101, 16:52, 17:27, 18:13, 19:7, 20:3, 21:2, 22:1
35178:3, 9:87, 10:378, 11:581, 12:516, 13:345, 14:199, 15:107, 16:56, 17:28, 18:14, 19:7, 20:4, 21:2, 22:1
368:3, 9:82, 10:375, 11:595, 12:537, 13:362, 14:210, 15:113, 16:59, 17:30, 18:15, 19:8, 20:4, 21:2, 22:1
37188:2, 9:77, 10:372, 11:609, 12:559, 13:380, 14:221, 15:120, 16:62, 17:32, 18:16, 19:8, 20:4, 21:2, 22:1, 23:1
388:2, 9:72, 10:368, 11:622, 12:580, 13:398, 14:233, 15:126, 16:66, 17:33, 18:17, 19:9, 20:4, 21:2, 22:1, 23:1
39198:2, 9:67, 10:364, 11:634, 12:602, 13:416, 14:245, 15:133, 16:69, 17:35, 18:18, 19:9, 20:5, 21:2, 22:1, 23:1
408:1, 9:63, 10:359, 11:646, 12:623, 13:434, 14:257, 15:139, 16:73, 17:37, 18:19, 19:9, 20:5, 21:2, 22:1, 23:1
41208:1, 9:59, 10:354, 11:657, 12:644, 13:453, 14:269, 15:146, 16:76, 17:39, 18:20, 19:10, 20:5, 21:3, 22:1, 23:1
428:1, 9:55, 10:349, 11:667, 12:665, 13:472, 14:281, 15:153, 16:80, 17:41, 18:21, 19:10, 20:5, 21:3, 22:1, 23:1
43218:1, 9:51, 10:343, 11:677, 12:686, 13:491, 14:294, 15:161, 16:84, 17:43, 18:22, 19:11, 20:6, 21:3, 22:1, 23:1
448:1, 9:48, 10:337, 11:686, 12:707, 13:510, 14:307, 15:168, 16:88, 17:45, 18:23, 19:12, 20:6, 21:3, 22:1, 23:1
45228:1, 9:44, 10:331, 11:694, 12:727, 13:530, 14:320, 15:176, 16:92, 17:47, 18:24, 19:12, 20:6, 21:3, 22:2, 23:1
469:41, 10:325, 11:702, 12:748, 13:549, 14:333, 15:183, 16:96, 17:49, 18:25, 19:13, 20:6, 21:3, 22:2, 23:1
47239:38, 10:319, 11:710, 12:768, 13:569, 14:346, 15:191, 16:100, 17:52, 18:26, 19:13, 20:7, 21:3, 22:2, 23:1
489:36, 10:312, 11:717, 12:788, 13:589, 14:360, 15:199, 16:105, 17:54, 18:27, 19:14, 20:7, 21:3, 22:2, 23:1
49249:33, 10:306, 11:723, 12:808, 13:609, 14:374, 15:207, 16:109, 17:56, 18:28, 19:14, 20:7, 21:4, 22:2, 23:1
509:31, 10:299, 11:729, 12:828, 13:629, 14:388, 15:215, 16:114, 17:58, 18:30, 19:15, 20:8, 21:4, 22:2, 23:1
51259:28, 10:292, 11:734, 12:848, 13:649, 14:402, 15:224, 16:118, 17:61, 18:31, 19:16, 20:8, 21:4, 22:2, 23:1
529:26, 10:286, 11:738, 12:867, 13:670, 14:417, 15:232, 16:123, 17:63, 18:32, 19:16, 20:8, 21:4, 22:2, 23:1, 24:1
53269:24, 10:279, 11:743, 12:886, 13:690, 14:432, 15:241, 16:128, 17:66, 18:33, 19:17, 20:8, 21:4, 22:2, 23:1, 24:1
549:23, 10:272, 11:746, 12:905, 13:711, 14:446, 15:250, 16:132, 17:68, 18:35, 19:17, 20:9, 21:4, 22:2, 23:1, 24:1
55279:21, 10:265, 11:749, 12:923, 13:732, 14:461, 15:259, 16:137, 17:71, 18:36, 19:18, 20:9, 21:5, 22:2, 23:1, 24:1
569:19, 10:259, 11:752, 12:942, 13:752, 14:476, 15:268, 16:142, 17:73, 18:37, 19:19, 20:9, 21:5, 22:2, 23:1, 24:1
57289:18, 10:252, 11:754, 12:960, 13:773, 14:492, 15:277, 16:147, 17:76, 18:39, 19:20, 20:10, 21:5, 22:2, 23:1, 24:1
589:17, 10:245, 11:756, 12:977, 13:794, 14:507, 15:287, 16:153, 17:79, 18:40, 19:20, 20:10, 21:5, 22:3, 23:1, 24:1
59299:15, 10:239, 11:757, 12:995, 13:815, 14:523, 15:296, 16:158, 17:81, 18:41, 19:21, 20:11, 21:5, 22:3, 23:1, 24:1
609:14, 10:233, 11:758, 12:1012, 13:836, 14:539, 15:306, 16:163, 17:84, 18:43, 19:22, 20:11, 21:5, 22:3, 23:1, 24:1
61309:13, 10:226, 11:759, 12:1029, 13:858, 14:555, 15:316, 16:168, 17:87, 18:44, 19:22, 20:11, 21:6, 22:3, 23:1, 24:1
629:12, 10:220, 11:759, 12:1046, 13:879, 14:571, 15:326, 16:174, 17:90, 18:46, 19:23, 20:12, 21:6, 22:3, 23:1, 24:1
63319:11, 10:214, 11:759, 12:1062, 13:900, 14:587, 15:336, 16:180, 17:93, 18:47, 19:24, 20:12, 21:6, 22:3, 23:1, 24:1
649:10, 10:207, 11:758, 12:1078, 13:921, 14:604, 15:346, 16:185, 17:96, 18:49, 19:25, 20:12, 21:6, 22:3, 23:2, 24:1
65329:10, 10:201, 11:757, 12:1094, 13:943, 14:620, 15:356, 16:191, 17:99, 18:50, 19:25, 20:13, 21:6, 22:3, 23:2, 24:1
669:9, 10:195, 11:756, 12:1109, 13:964, 14:637, 15:367, 16:197, 17:102, 18:52, 19:26, 20:13, 21:7, 22:3, 23:2, 24:1
67339:8, 10:190, 11:754, 12:1125, 13:985, 14:654, 15:377, 16:203, 17:105, 18:53, 19:27, 20:14, 21:7, 22:3, 23:2, 24:1
689:8, 10:184, 11:752, 12:1139, 13:1007, 14:671, 15:388, 16:209, 17:108, 18:55, 19:28, 20:14, 21:7, 22:3, 23:2, 24:1
69349:7, 10:178, 11:750, 12:1154, 13:1028, 14:689, 15:399, 16:215, 17:111, 18:57, 19:29, 20:14, 21:7, 22:4, 23:2, 24:1
709:6, 10:173, 11:748, 12:1168, 13:1049, 14:706, 15:410, 16:221, 17:115, 18:58, 19:30, 20:15, 21:7, 22:4, 23:2, 24:1
71359:6, 10:168, 11:745, 12:1182, 13:1071, 14:723, 15:421, 16:227, 17:118, 18:60, 19:30, 20:15, 21:8, 22:4, 23:2, 24:1
729:5, 10:162, 11:742, 12:1196, 13:1092, 14:741, 15:432, 16:233, 17:121, 18:62, 19:31, 20:16, 21:8, 22:4, 23:2, 24:1
73369:5, 10:157, 11:739, 12:1209, 13:1114, 14:759, 15:443, 16:240, 17:125, 18:63, 19:32, 20:16, 21:8, 22:4, 23:2, 24:1, 25:1
749:5, 10:152, 11:735, 12:1222, 13:1135, 14:776, 15:455, 16:246, 17:128, 18:65, 19:33, 20:17, 21:8, 22:4, 23:2, 24:1, 25:1
75379:4, 10:147, 11:731, 12:1234, 13:1156, 14:794, 15:466, 16:253, 17:132, 18:67, 19:34, 20:17, 21:9, 22:4, 23:2, 24:1, 25:1
769:4, 10:143, 11:727, 12:1247, 13:1177, 14:812, 15:478, 16:259, 17:135, 18:69, 19:35, 20:18, 21:9, 22:4, 23:2, 24:1, 25:1
77389:4, 10:138, 11:723, 12:1259, 13:1199, 14:830, 15:490, 16:266, 17:139, 18:71, 19:36, 20:18, 21:9, 22:5, 23:2, 24:1, 25:1
789:3, 10:134, 11:719, 12:1271, 13:1220, 14:849, 15:502, 16:273, 17:142, 18:73, 19:37, 20:19, 21:9, 22:5, 23:2, 24:1, 25:1
79399:3, 10:129, 11:714, 12:1282, 13:1241, 14:867, 15:514, 16:279, 17:146, 18:74, 19:38, 20:19, 21:9, 22:5, 23:2, 24:1, 25:1
809:3, 10:125, 11:710, 12:1294, 13:1262, 14:886, 15:526, 16:286, 17:150, 18:76, 19:39, 20:20, 21:10, 22:5, 23:2, 24:1, 25:1
81409:3, 10:121, 11:705, 12:1304, 13:1283, 14:904, 15:538, 16:293, 17:153, 18:78, 19:40, 20:20, 21:10, 22:5, 23:2, 24:1, 25:1
829:2, 10:117, 11:700, 12:1315, 13:1304, 14:923, 15:550, 16:300, 17:157, 18:80, 19:41, 20:21, 21:10, 22:5, 23:3, 24:1, 25:1
83419:2, 10:113, 11:695, 12:1325, 13:1325, 14:942, 15:563, 16:308, 17:161, 18:82, 19:42, 20:21, 21:10, 22:5, 23:3, 24:1, 25:1
849:2, 10:109, 11:689, 12:1335, 13:1346, 14:961, 15:575, 16:315, 17:165, 18:84, 19:43, 20:22, 21:11, 22:5, 23:3, 24:1, 25:1
85429:2, 10:105, 11:684, 12:1345, 13:1367, 14:980, 15:588, 16:322, 17:169, 18:86, 19:44, 20:22, 21:11, 22:6, 23:3, 24:1, 25:1
869:2, 10:102, 11:678, 12:1354, 13:1387, 14:999, 15:601, 16:329, 17:173, 18:88, 19:45, 20:23, 21:11, 22:6, 23:3, 24:1, 25:1
87439:2, 10:98, 11:673, 12:1363, 13:1408, 14:1018, 15:614, 16:337, 17:177, 18:90, 19:46, 20:23, 21:12, 22:6, 23:3, 24:1, 25:1
889:2, 10:95, 11:667, 12:1371, 13:1429, 14:1038, 15:627, 16:344, 17:181, 18:92, 19:47, 20:24, 21:12, 22:6, 23:3, 24:1, 25:1
89449:1, 10:92, 11:661, 12:1380, 13:1449, 14:1057, 15:640, 16:352, 17:185, 18:95, 19:48, 20:24, 21:12, 22:6, 23:3, 24:1, 25:1
909:1, 10:88, 11:655, 12:1388, 13:1470, 14:1076, 15:653, 16:360, 17:189, 18:97, 19:49, 20:25, 21:12, 22:6, 23:3, 24:2, 25:1
91459:1, 10:85, 11:649, 12:1396, 13:1490, 14:1096, 15:666, 16:367, 17:193, 18:99, 19:50, 20:25, 21:13, 22:6, 23:3, 24:2, 25:1
929:1, 10:82, 11:643, 12:1403, 13:1511, 14:1116, 15:680, 16:375, 17:197, 18:101, 19:51, 20:26, 21:13, 22:6, 23:3, 24:2, 25:1
93469:1, 10:79, 11:637, 12:1411, 13:1531, 14:1135, 15:693, 16:383, 17:201, 18:103, 19:52, 20:26, 21:13, 22:7, 23:3, 24:2, 25:1
949:1, 10:77, 11:630, 12:1418, 13:1551, 14:1155, 15:707, 16:391, 17:206, 18:105, 19:53, 20:27, 21:13, 22:7, 23:3, 24:2, 25:1
95479:1, 10:74, 11:624, 12:1425, 13:1571, 14:1175, 15:721, 16:399, 17:210, 18:108, 19:55, 20:28, 21:14, 22:7, 23:3, 24:2, 25:1
969:1, 10:71, 11:618, 12:1431, 13:1591, 14:1195, 15:734, 16:407, 17:215, 18:110, 19:56, 20:28, 21:14, 22:7, 23:4, 24:2, 25:1
97489:1, 10:69, 11:611, 12:1437, 13:1610, 14:1215, 15:748, 16:415, 17:219, 18:112, 19:57, 20:29, 21:14, 22:7, 23:4, 24:2, 25:1
989:1, 10:66, 11:605, 12:1443, 13:1630, 14:1235, 15:762, 16:423, 17:223, 18:115, 19:58, 20:29, 21:15, 22:7, 23:4, 24:2, 25:1
99499:1, 10:64, 11:598, 12:1449, 13:1650, 14:1255, 15:776, 16:432, 17:228, 18:117, 19:59, 20:30, 21:15, 22:7, 23:4, 24:2, 25:1
1009:1, 10:62, 11:592, 12:1454, 13:1669, 14:1275, 15:791, 16:440, 17:232, 18:119, 19:60, 20:31, 21:15, 22:8, 23:4, 24:2, 25:1

For males, the constant 6:1 is from one ancestor contributing 1/46th of the DNA, namely the Y chromosome along the direct paternal line. There are a few strongly related individuals for females too, due to X having crossovers about every other generation.

How many ancestors X generations gave closest to 2-Y of your DNA from (starting from a male):
generationnth cousinsY:Z, where Z ancestors gave closest to 2-Y of the DNA
00:1
1siblings1:2
22:4
31st cousins3:7, 4:1
43:1, 4:12, 5:2
52nd cousins4:5, 5:19, 6:7, 7:1
65:13, 6:29, 7:15, 8:4, 9:1
73rd cousins5:3, 6:28, 7:44, 8:27, 9:12, 10:5, 11:2, 12:1, 13:1
85:1, 6:13, 7:55, 8:63, 9:42, 10:22, 11:11, 12:6, 13:3, 14:1, 15:1
94th cousins5:1, 6:5, 7:44, 8:90, 9:83, 10:54, 11:31, 12:16, 13:8, 14:4, 15:2, 16:1, 17:1
106:2, 7:29, 8:98, 9:121, 10:93, 11:57, 12:32, 13:17, 14:8, 15:4, 16:2, 17:1, 18:1
115th cousins6:1, 7:18, 8:95, 9:150, 10:130, 11:86, 12:49, 13:26, 14:13, 15:7, 16:3, 17:2, 18:1
126:1, 7:11, 8:87, 9:168, 10:164, 11:114, 12:67, 13:36, 14:19, 15:10, 16:5, 17:2, 18:1, 19:1
136th cousins6:1, 7:7, 8:78, 9:180, 10:192, 11:140, 12:85, 13:46, 14:24, 15:12, 16:6, 17:3, 18:2, 19:1
146:1, 7:5, 8:69, 9:187, 10:217, 11:165, 12:102, 13:56, 14:30, 15:15, 16:8, 17:4, 18:2, 19:1
157th cousins6:1, 7:3, 8:61, 9:190, 10:238, 11:188, 12:119, 13:66, 14:35, 15:18, 16:9, 17:5, 18:2, 19:1, 20:1
166:1, 7:2, 8:53, 9:191, 10:257, 11:211, 12:136, 13:77, 14:41, 15:21, 16:11, 17:5, 18:3, 19:1, 20:1
178th cousins6:1, 7:1, 8:47, 9:190, 10:274, 11:233, 12:153, 13:87, 14:46, 15:24, 16:12, 17:6, 18:3, 19:2, 20:1
186:1, 7:1, 8:41, 9:187, 10:289, 11:255, 12:170, 13:98, 14:52, 15:27, 16:14, 17:7, 18:3, 19:2, 20:1
199th cousins6:1, 7:1, 8:35, 9:184, 10:303, 11:276, 12:188, 13:109, 14:59, 15:30, 16:16, 17:8, 18:4, 19:2, 20:1, 21:1
206:1, 8:31, 9:179, 10:316, 11:298, 12:206, 13:121, 14:65, 15:34, 16:17, 17:9, 18:4, 19:2, 20:1, 21:1
21106:1, 8:27, 9:174, 10:327, 11:319, 12:224, 13:133, 14:72, 15:38, 16:19, 17:10, 18:5, 19:2, 20:1, 21:1
226:1, 8:23, 9:168, 10:336, 11:340, 12:243, 13:145, 14:79, 15:41, 16:21, 17:11, 18:5, 19:3, 20:1, 21:1
23116:1, 8:20, 9:162, 10:345, 11:360, 12:262, 13:158, 14:86, 15:45, 16:23, 17:12, 18:6, 19:3, 20:1, 21:1
246:1, 8:17, 9:156, 10:352, 11:381, 12:281, 13:171, 14:94, 15:49, 16:25, 17:13, 18:6, 19:3, 20:2, 21:1
25126:1, 8:14, 9:149, 10:359, 11:400, 12:301, 13:185, 14:102, 15:54, 16:28, 17:14, 18:7, 19:4, 20:2, 21:1
266:1, 8:12, 9:142, 10:364, 11:420, 12:321, 13:199, 14:110, 15:58, 16:30, 17:15, 18:8, 19:4, 20:2, 21:1
27136:1, 8:11, 9:135, 10:368, 11:439, 12:341, 13:213, 14:119, 15:63, 16:32, 17:16, 18:8, 19:4, 20:2, 21:1, 22:1
286:1, 8:9, 9:128, 10:371, 11:457, 12:362, 13:228, 14:128, 15:68, 16:35, 17:18, 18:9, 19:4, 20:2, 21:1, 22:1
29146:1, 8:8, 9:122, 10:373, 11:475, 12:383, 13:243, 14:137, 15:73, 16:37, 17:19, 18:10, 19:5, 20:2, 21:1, 22:1
306:1, 8:6, 9:115, 10:374, 11:492, 12:403, 13:258, 14:146, 15:78, 16:40, 17:20, 18:10, 19:5, 20:3, 21:1, 22:1
31156:1, 8:5, 9:108, 10:375, 11:509, 12:424, 13:274, 14:156, 15:83, 16:43, 17:22, 18:11, 19:5, 20:3, 21:1, 22:1
326:1, 8:5, 9:102, 10:375, 11:525, 12:445, 13:290, 14:166, 15:88, 16:46, 17:23, 18:12, 19:6, 20:3, 21:1, 22:1
33166:1, 8:4, 9:96, 10:373, 11:541, 12:466, 13:306, 14:176, 15:94, 16:49, 17:25, 18:12, 19:6, 20:3, 21:2, 22:1
346:1, 8:3, 9:90, 10:372, 11:556, 12:487, 13:323, 14:186, 15:100, 16:52, 17:26, 18:13, 19:7, 20:3, 21:2, 22:1
35176:1, 8:3, 9:85, 10:370, 11:570, 12:508, 13:340, 14:197, 15:106, 16:55, 17:28, 18:14, 19:7, 20:4, 21:2, 22:1
366:1, 8:2, 9:79, 10:367, 11:584, 12:529, 13:357, 14:207, 15:112, 16:58, 17:30, 18:15, 19:7, 20:4, 21:2, 22:1
37186:1, 8:2, 9:74, 10:363, 11:597, 12:550, 13:374, 14:218, 15:118, 16:61, 17:31, 18:16, 19:8, 20:4, 21:2, 22:1
386:1, 8:2, 9:70, 10:360, 11:610, 12:571, 13:392, 14:230, 15:124, 16:65, 17:33, 18:17, 19:8, 20:4, 21:2, 22:1, 23:1
39196:1, 8:1, 9:65, 10:355, 11:622, 12:592, 13:410, 14:241, 15:131, 16:68, 17:35, 18:18, 19:9, 20:4, 21:2, 22:1, 23:1
406:1, 8:1, 9:61, 10:351, 11:633, 12:613, 13:428, 14:253, 15:138, 16:72, 17:37, 18:18, 19:9, 20:5, 21:2, 22:1, 23:1
41206:1, 8:1, 9:57, 10:346, 11:644, 12:634, 13:446, 14:265, 15:144, 16:75, 17:39, 18:19, 19:10, 20:5, 21:2, 22:1, 23:1
426:1, 8:1, 9:53, 10:340, 11:654, 12:655, 13:465, 14:277, 15:151, 16:79, 17:40, 18:20, 19:10, 20:5, 21:3, 22:1, 23:1
43216:1, 8:1, 9:49, 10:335, 11:664, 12:675, 13:484, 14:290, 15:159, 16:83, 17:42, 18:21, 19:11, 20:5, 21:3, 22:1, 23:1
446:1, 8:1, 9:46, 10:329, 11:672, 12:695, 13:503, 14:303, 15:166, 16:87, 17:44, 18:22, 19:11, 20:6, 21:3, 22:1, 23:1
45226:1, 9:42, 10:323, 11:681, 12:716, 13:522, 14:315, 15:173, 16:91, 17:46, 18:23, 19:12, 20:6, 21:3, 22:1, 23:1
466:1, 9:39, 10:317, 11:688, 12:736, 13:541, 14:328, 15:181, 16:95, 17:49, 18:25, 19:12, 20:6, 21:3, 22:2, 23:1
47236:1, 9:37, 10:311, 11:696, 12:756, 13:560, 14:342, 15:189, 16:99, 17:51, 18:26, 19:13, 20:6, 21:3, 22:2, 23:1
486:1, 9:34, 10:304, 11:702, 12:775, 13:580, 14:355, 15:197, 16:103, 17:53, 18:27, 19:13, 20:7, 21:3, 22:2, 23:1
49246:1, 9:32, 10:298, 11:708, 12:795, 13:600, 14:369, 15:205, 16:108, 17:55, 18:28, 19:14, 20:7, 21:4, 22:2, 23:1
506:1, 9:29, 10:291, 11:714, 12:814, 13:619, 14:383, 15:213, 16:112, 17:58, 18:29, 19:15, 20:7, 21:4, 22:2, 23:1
51256:1, 9:27, 10:285, 11:719, 12:834, 13:639, 14:397, 15:221, 16:117, 17:60, 18:30, 19:15, 20:8, 21:4, 22:2, 23:1
526:1, 9:25, 10:278, 11:723, 12:852, 13:659, 14:411, 15:230, 16:121, 17:62, 18:32, 19:16, 20:8, 21:4, 22:2, 23:1
53266:1, 9:23, 10:272, 11:727, 12:871, 13:679, 14:425, 15:238, 16:126, 17:65, 18:33, 19:16, 20:8, 21:4, 22:2, 23:1, 24:1
546:1, 9:22, 10:265, 11:731, 12:889, 13:700, 14:440, 15:247, 16:131, 17:67, 18:34, 19:17, 20:9, 21:4, 22:2, 23:1, 24:1
55276:1, 9:20, 10:258, 11:734, 12:908, 13:720, 14:455, 15:256, 16:136, 17:70, 18:35, 19:18, 20:9, 21:4, 22:2, 23:1, 24:1
566:1, 9:18, 10:252, 11:736, 12:926, 13:741, 14:470, 15:265, 16:141, 17:72, 18:37, 19:18, 20:9, 21:5, 22:2, 23:1, 24:1
57286:1, 9:17, 10:245, 11:738, 12:943, 13:761, 14:485, 15:274, 16:145, 17:75, 18:38, 19:19, 20:10, 21:5, 22:2, 23:1, 24:1
586:1, 9:16, 10:239, 11:740, 12:961, 13:782, 14:500, 15:283, 16:151, 17:78, 18:39, 19:20, 20:10, 21:5, 22:3, 23:1, 24:1
59296:1, 9:15, 10:232, 11:741, 12:978, 13:803, 14:516, 15:292, 16:156, 17:80, 18:41, 19:20, 20:10, 21:5, 22:3, 23:1, 24:1
606:1, 9:13, 10:226, 11:742, 12:994, 13:823, 14:531, 15:302, 16:161, 17:83, 18:42, 19:21, 20:11, 21:5, 22:3, 23:1, 24:1
61306:1, 9:12, 10:220, 11:743, 12:1011, 13:844, 14:547, 15:312, 16:166, 17:86, 18:44, 19:22, 20:11, 21:6, 22:3, 23:1, 24:1
626:1, 9:11, 10:214, 11:743, 12:1027, 13:865, 14:563, 15:321, 16:172, 17:89, 18:45, 19:23, 20:11, 21:6, 22:3, 23:1, 24:1
63316:1, 9:11, 10:207, 11:742, 12:1043, 13:886, 14:579, 15:331, 16:177, 17:92, 18:47, 19:23, 20:12, 21:6, 22:3, 23:2, 24:1
646:1, 9:10, 10:201, 11:742, 12:1059, 13:906, 14:595, 15:341, 16:183, 17:95, 18:48, 19:24, 20:12, 21:6, 22:3, 23:2, 24:1
65326:1, 9:9, 10:196, 11:741, 12:1075, 13:927, 14:612, 15:351, 16:188, 17:98, 18:50, 19:25, 20:13, 21:6, 22:3, 23:2, 24:1
666:1, 9:8, 10:190, 11:739, 12:1090, 13:948, 14:628, 15:362, 16:194, 17:101, 18:51, 19:26, 20:13, 21:6, 22:3, 23:2, 24:1
67336:1, 9:8, 10:184, 11:738, 12:1104, 13:969, 14:645, 15:372, 16:200, 17:104, 18:53, 19:27, 20:13, 21:7, 22:3, 23:2, 24:1
686:1, 9:7, 10:178, 11:736, 12:1119, 13:990, 14:662, 15:383, 16:206, 17:107, 18:54, 19:27, 20:14, 21:7, 22:3, 23:2, 24:1
69346:1, 9:7, 10:173, 11:734, 12:1133, 13:1011, 14:679, 15:393, 16:212, 17:110, 18:56, 19:28, 20:14, 21:7, 22:4, 23:2, 24:1
706:1, 9:6, 10:168, 11:731, 12:1147, 13:1032, 14:696, 15:404, 16:218, 17:113, 18:58, 19:29, 20:15, 21:7, 22:4, 23:2, 24:1
71356:1, 9:6, 10:162, 11:728, 12:1161, 13:1053, 14:713, 15:415, 16:224, 17:116, 18:59, 19:30, 20:15, 21:8, 22:4, 23:2, 24:1
726:1, 9:5, 10:157, 11:725, 12:1174, 13:1074, 14:730, 15:426, 16:230, 17:120, 18:61, 19:31, 20:15, 21:8, 22:4, 23:2, 24:1
73366:1, 9:5, 10:152, 11:722, 12:1187, 13:1095, 14:748, 15:437, 16:236, 17:123, 18:63, 19:32, 20:16, 21:8, 22:4, 23:2, 24:1, 25:1
746:1, 9:4, 10:147, 11:719, 12:1200, 13:1116, 14:765, 15:448, 16:243, 17:126, 18:64, 19:33, 20:16, 21:8, 22:4, 23:2, 24:1, 25:1
75376:1, 9:4, 10:143, 11:715, 12:1212, 13:1137, 14:783, 15:460, 16:249, 17:130, 18:66, 19:33, 20:17, 21:8, 22:4, 23:2, 24:1, 25:1
766:1, 9:4, 10:138, 11:711, 12:1224, 13:1158, 14:801, 15:471, 16:256, 17:133, 18:68, 19:34, 20:17, 21:9, 22:4, 23:2, 24:1, 25:1
77386:1, 9:3, 10:133, 11:707, 12:1236, 13:1179, 14:819, 15:483, 16:262, 17:137, 18:70, 19:35, 20:18, 21:9, 22:4, 23:2, 24:1, 25:1
786:1, 9:3, 10:129, 11:703, 12:1247, 13:1200, 14:837, 15:494, 16:269, 17:140, 18:72, 19:36, 20:18, 21:9, 22:5, 23:2, 24:1, 25:1
79396:1, 9:3, 10:125, 11:698, 12:1258, 13:1221, 14:855, 15:506, 16:276, 17:144, 18:73, 19:37, 20:19, 21:9, 22:5, 23:2, 24:1, 25:1
806:1, 9:3, 10:121, 11:694, 12:1269, 13:1241, 14:873, 15:518, 16:282, 17:147, 18:75, 19:38, 20:19, 21:10, 22:5, 23:2, 24:1, 25:1
81406:1, 9:2, 10:116, 11:689, 12:1280, 13:1262, 14:891, 15:530, 16:289, 17:151, 18:77, 19:39, 20:20, 21:10, 22:5, 23:3, 24:1, 25:1
826:1, 9:2, 10:113, 11:684, 12:1290, 13:1283, 14:910, 15:542, 16:296, 17:155, 18:79, 19:40, 20:20, 21:10, 22:5, 23:3, 24:1, 25:1
83416:1, 9:2, 10:109, 11:679, 12:1300, 13:1303, 14:928, 15:555, 16:303, 17:159, 18:81, 19:41, 20:21, 21:10, 22:5, 23:3, 24:1, 25:1
846:1, 9:2, 10:105, 11:673, 12:1310, 13:1324, 14:947, 15:567, 16:310, 17:162, 18:83, 19:42, 20:21, 21:11, 22:5, 23:3, 24:1, 25:1
85426:1, 9:2, 10:101, 11:668, 12:1319, 13:1344, 14:966, 15:580, 16:318, 17:166, 18:85, 19:43, 20:22, 21:11, 22:5, 23:3, 24:1, 25:1
866:1, 9:2, 10:98, 11:662, 12:1328, 13:1364, 14:985, 15:592, 16:325, 17:170, 18:87, 19:44, 20:22, 21:11, 22:6, 23:3, 24:1, 25:1
87436:1, 9:1, 10:95, 11:657, 12:1337, 13:1385, 14:1004, 15:605, 16:332, 17:174, 18:89, 19:45, 20:23, 21:11, 22:6, 23:3, 24:1, 25:1
886:1, 9:1, 10:91, 11:651, 12:1345, 13:1405, 14:1023, 15:618, 16:339, 17:178, 18:91, 19:46, 20:23, 21:12, 22:6, 23:3, 24:1, 25:1
89446:1, 9:1, 10:88, 11:645, 12:1353, 13:1425, 14:1042, 15:631, 16:347, 17:182, 18:93, 19:47, 20:24, 21:12, 22:6, 23:3, 24:1, 25:1
906:1, 9:1, 10:85, 11:639, 12:1361, 13:1445, 14:1061, 15:644, 16:354, 17:186, 18:95, 19:48, 20:24, 21:12, 22:6, 23:3, 24:2, 25:1
91456:1, 9:1, 10:82, 11:633, 12:1369, 13:1465, 14:1080, 15:657, 16:362, 17:190, 18:97, 19:49, 20:25, 21:12, 22:6, 23:3, 24:2, 25:1
926:1, 9:1, 10:79, 11:627, 12:1376, 13:1485, 14:1099, 15:670, 16:370, 17:194, 18:100, 19:50, 20:25, 21:13, 22:6, 23:3, 24:2, 25:1
93466:1, 9:1, 10:76, 11:621, 12:1383, 13:1505, 14:1119, 15:683, 16:378, 17:199, 18:102, 19:51, 20:26, 21:13, 22:6, 23:3, 24:2, 25:1
946:1, 9:1, 10:74, 11:615, 12:1390, 13:1524, 14:1138, 15:697, 16:385, 17:203, 18:104, 19:53, 20:26, 21:13, 22:7, 23:3, 24:2, 25:1
95476:1, 9:1, 10:71, 11:609, 12:1396, 13:1544, 14:1158, 15:710, 16:393, 17:207, 18:106, 19:54, 20:27, 21:14, 22:7, 23:3, 24:2, 25:1
966:1, 9:1, 10:68, 11:602, 12:1403, 13:1563, 14:1178, 15:724, 16:401, 17:211, 18:109, 19:55, 20:28, 21:14, 22:7, 23:4, 24:2, 25:1
97486:1, 9:1, 10:66, 11:596, 12:1409, 13:1583, 14:1197, 15:737, 16:409, 17:216, 18:111, 19:56, 20:28, 21:14, 22:7, 23:4, 24:2, 25:1
986:1, 9:1, 10:64, 11:590, 12:1414, 13:1602, 14:1217, 15:751, 16:417, 17:220, 18:113, 19:57, 20:29, 21:14, 22:7, 23:4, 24:2, 25:1
99496:1, 9:1, 10:61, 11:583, 12:1420, 13:1621, 14:1237, 15:765, 16:426, 17:225, 18:115, 19:58, 20:29, 21:15, 22:7, 23:4, 24:2, 25:1
1006:1, 10:59, 11:577, 12:1425, 13:1640, 14:1257, 15:779, 16:434, 17:229, 18:118, 19:60, 20:30, 21:15, 22:8, 23:4, 24:2, 25:1

Miscellaneous observations

I used 23andMe's genetic testing for me and my family, and found a cousin I share 0.31% of my DNA with. However, my son shares 0.48% of his DNA with that same cousin. How can that be? Does that mean my wife and I are closely related? Probably not. More likely, I'm a distant cousin on his mother's side, and my wife is a distant cousin on his father's side. That doesn't imply that my wife and I are related at all, yet it still allows our son to have more DNA in common with him than either of us has.

The small number of genetic ancestors implies it is much easier to not be inbred according to genetic ancestors than by genealogical ancestors. You had a trillion genealogical ancestors 40 generations back, which far exceeds the total number of people who have ever existed, so most of your ancestors appear many many times in your genealogical tree. But you had under 3000 genetic ancestors 40 generations back (and under 7000 at 100 generations back). It's quite feasible for all your genetic ancestors to have been distinct for as far back as it's practical to go.

I wonder what the mechanical process is for meiosis. It sounds you get two pairs, then you exchange the ends of one side of each of those pairs to force crossover. Maybe the other ends are twisted around, or moved independently in a fixed manner. I don't know if both ends are twisted or just one end, but the middle doesn't seem to be moved in a controlled manner.


Bob Predicts the Future

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