0:00 what does genetic drift you've heard
0:02 that before what is it it's just what's
0:06 the word stochastic mean have you heard
0:09 that word before stochastic effect
0:12 probably heard with respect to PCR if
0:17 you have for red socks and four black
0:20 socks in a drawer and you randomly go in
0:24 and pick one what's the chance of
0:25 getting one or the other 50% right if
0:29 you have one in one what's the chances
0:32 still 50% but if you're picking out one
0:35 by chance and copying it if you only
0:38 have two to choose from the chance is
0:41 still 50% but if you start copying that
0:43 black one it's going to appear like
0:46 there's more black socks than there are
0:47 red socks because you just by chance
0:49 chose that one black sock but if you had
0:52 300,000 of each in the drawer and you
0:54 picked it it's still you know remember
0:57 PCR you're picking a bunch at the same
0:59 time in algae but the point being that
1:02 if you pick one and it's very very
1:06 little to start you might get an
1:08 incorrect representation of how many are
1:10 actually what the proportion between
1:11 them actually are and that is in this
1:14 sense the heterozygotes right you might
1:16 have one peak way up here and there
1:17 another one down here which would
1:20 falsely indicate there's more of this
1:22 than this it's just because you weren't
1:23 choosing very many to choose from in the
1:25 beginning stages of the PCR stochastic
1:28 effect stochastic meaning just by chance
1:32 fluctuation that's the same thing with
1:35 genetic drift alleles become fixed in
1:39 populations when I say fixed I mean
1:43 common enough that they're seen in a lot
1:45 of people that is more than one percent
1:48 sometimes just by genetic drift by
1:54 chance
