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 Lecture on Genetic Drift

January 9, 2019
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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
    
  
Disclaimer:
              Opinions or points of view expressed in these recordings represent those of the speakers and do not necessarily represent the official position or policies of the U.S. Department of Justice. Any commercial products and manufacturers discussed in these recordings are presented for informational purposes only and do not constitute product approval or endorsement by the U.S. Department of Justice.
  
Date Published: January 9, 2019
    
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