Half of our chromosomes come from mom, half from dad.
*On average* one quarter come from each grandparent, but obviously there is no integer solution to one quarter of 46, so the concentration of genetic origin begins with the grandparental generation, and it turns into something analogous to the old "war" card game -- an early advantage means eventual victory. Here's some arbitrarily and randomly assigned values, showing the pathway to the 46 of the current hypothetical person (but entirely possible, and given the 2^23 squared possibilities in each generation, this is bound to have happened at least once by now, to someone, somewhere):
| 0 |
0 |
0 |
1 |
2 |
1 |
0 |
1 |
1 |
0 |
1 |
2 |
0 |
1 |
0 |
0 |
3 |
1 |
2 |
2 |
1 |
0 |
0 |
1 |
0 |
0 |
1 |
0 |
1 |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
0 |
1 |
3 |
0 |
2 |
1 |
1 |
0 |
1 |
0 |
1 |
2 |
1 |
1 |
0 |
1 |
0 |
0 |
1 |
0 |
0 |
1 |
2 |
2 |
0 |
| 0 |
1 |
3 |
1 |
1 |
3 |
1 |
0 |
4 |
4 |
1 |
1 |
0 |
1 |
2 |
0 |
0 |
0 |
1 |
1 |
4 |
2 |
2 |
1 |
1 |
3 |
1 |
1 |
1 |
0 |
3 |
2 |
| 1 |
4 |
4 |
1 |
8 |
2 |
1 |
2 |
0 |
2 |
6 |
3 |
4 |
2 |
1 |
5 |
| 5 |
5 |
10 |
3 |
2 |
9 |
6 |
6 |
| 10 |
13 |
11 |
12 |
| 23 |
23 |
| 46 |
I started from 46 and worked back, but if we wanted to maximize the number of genetic sources from the 4ggrand generation (46 of 'em, of the 64 on the tree), we need only put zeroes in 18 of them at random, then carry the totals additively downward. Probably would be a lot easier than the pain in the neck I just went through with that. Hope I didn't miss any typos. And of course, the other way to do that is to do the actual family tree and see if there are any duplicate ancestors. :')