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 Lecture on Alleles with Low Frequencies

January 9, 2019
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          Transcript
0:00

what happens when you get an allele at a

0:04

locus for one of your markers that has

0:07

an allele frequency of zero if you're

0:11

using pop stands what does it do

0:15

right how do you know its use that in

0:18

pop stats

0:19

oh how do you know then they put the

0:30

number in for you correct there's a

0:34

little M that they print out beside the

0:38

allele you'll see an M that means

0:44

minimum allele frequency and there are

0:48

different ways of calculating it I did a

0:51

bunch of research on this when we were

0:53

trying to get our SOP written for how to

0:56

do this in Denver so I did a little bit

0:59

of research and I found that there's

1:02

actually three three ways of doing it

1:04

that are published first is using two

1:08

pieces of information the Alpha level

1:10

which is your level of confidence right

1:12

95 percent or 5 percent so alpha would

1:15

be 5% if you want to be 99 or 95%

1:18

confident 1% if you wanted to be 99

1:21

percent confident and is the number of

1:24

people in your database okay you know

1:28

that for each group that sometimes

1:30

varies that varies between the groups

1:33

right different number of people so the

1:35

first one from 1992 takes into effect

1:39

accounts for the level of confidence and

1:42

the number of people in the database

1:43

that's the top formula there the next

1:46

one that came out International Journal

1:48

legal medicine in 96 it has a little bit

1:50

more information it uses the Alpha level

1:53

it uses the number of people in the

1:56

database but it also uses C which is the

2:00

number of common alleles at the locus I

2:03

chose that to use that in my when we

2:08

before we were using pop stats I chose

2:10

to use that form of

2:13

the minimum allele frequency because it

2:15

had the most information accounted for

2:18

right and then in NRC two they recommend

2:24

five over 2n okay so you guys are

2:28

critical thinkers what do you think

2:32

between these three what would you do

2:35

and how would you decide well the reason

2:42

I decided on the middle one when I did

2:43

was because it was published the other

2:46

two are as well one is in NRC 96 the

2:49

other ones in a 1992 book by weird I

2:51

chose the middle one because it had more

2:54

information it accounted for more in the

2:57

database right not just the number of

2:59

people but the number of common alleles

3:01

well as it turns out if you look at

3:07

different n sizes numbers of people in

3:10

the database and you look at the NRC to

3:13

5 over 2n you get about at the very top

3:19

0.025 right 150 people vote point oh one

3:26

seven 200 people about 0.01 most of our

3:32

databases that we're using are on the

3:33

order of about 200 people right so you

3:37

can see that 5 over 2 n gives whether

3:40

you have 200 people about 0.01 or 100

3:46

look at the difference between the 3

3:49

methods now over the same number okay

3:53

around 200 people

3:55

Weir's gives point zero zero seven five

3:59

well if you round that up what do you

4:01

get

4:05

what's the point 0 0 75 rounded up 0.01

4:10

right to the next decimal place

4:12

what about Bedok Lee's method that's the

4:16

International Journal legal medicine

4:18

1996 0.01

4:22

what about NRC to 5 over 2 N 1 ok that's

4:28

with the top with a minimum allele

4:31

frequency where alpha is 0.05 and you

4:33

have 8 alleles what about if you have

4:38

double the number of alleles you have 16

4:41

alleles now well what happens for about

4:44

200 people when you get think the

4:53

numbers are slightly different but the

4:54

practical significance isn't right get

4:57

about point or what
    
  
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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