Population Genetics

Question 1

Overall Population Genetics

Answer 1

All about Frequency – Frequency of alleles + Frequency of genotypes

Question 2

Why is it important to know Frequency (Ex)

Answer 2

Example – Important to know the Frequency of a disease causing allele

Question 3

Example – calculating Genotype Frequency

RR = 1
Rr = 3
rr = 6

Answer 3

Question 4

Sum of all genotype Frequency

Answer 4

1.0 – sum of all Frequency should add up to 1.0

Question 5

Example – calculating Allele Frequency

RR = 1
Rr = 3
rr = 6

Answer 5

Question 6

Calculating Allele Frequency (Overall)

Answer 6

Allele/Total # of alleles in population

Question 7

Sum of all allele Frequency

Answer 7

1.0 – sum of all allele = 1

Question 8

Crash Course Video

Answer 8

Look at notes

Question 9

H-W (Overall)

Answer 9

Describes that under the right circumstances mendelian genetics works at the whole populations

Question 10

What does H-W show?

Answer 10

Shows the Frequency with which to expect to find different alleles within the population thats not evolving
- States the equilibrium
- Frequncey of alleles in the popultions = remaining constant from generation to generation

Question 11

Allele frequency change in H-W

Answer 11

Frequency of alleles in the population = remain constant from generation to generation
- If the assumptions of H-W are met –> allele frequencies don’t change over time

Question 12

Requirements for H-W

Answer 12

1. No Natural Selection – no alleles are beneficial than any other
2. No Sexual selection – mating in population is random
   
   • No individual can have a better chance
3. No Mutations
4. Need huge population because smaller population have more genetic drift
5. No Gene flow – would mess with allele Frequency

Question 13

H- W equation

Answer 13

P^2 + 2pq + q^2 = 1.0

Question 14

Deriving H-W

Answer 14

Have P and Q

P = Frequncey of one allele
Q = Frequency of another allele

P + Q = 1.9

Frequncey of AA = P X P
- Multiple two because each individual has two alleles

Frequncey of Aa = 2pq

Frequncey of aa = q X q

Question 15

What does H-W show

Answer 15

Can see mendle’s laws ay work in a population

Question 16

What happens if frequencies don’t like up with equilibrium

Answer 16

If things don’t line up with equilibrium = know that there are some factors at work

Question 17

T/F – Dominant alleles will increase in frequency over time

Answer 17

False – Dominance has no influence in increase unless it has selective pressure

Question 18

History

Answer 18

1905 – Punnet have punnets square to describe mendelian ratios
- Looked at way to predict mendelian ratios with punnet square

–> Student asked Punnet – If brown eyes are dominant to blue then why isn’t all of population becoming brown eyed –> He didn’t know the answer

1915 – TH Morgan looking at white eyed flies and sex linkage

Question 19

Issue Punnet had

Answer 19

He could not answer question of why Dominant traits do not always increase in Frequency over time

Didn’t know why dominant alleles don’t take over populations

Question 20

Why did people push against Mendle

Answer 20

People pushed against Mendle because thought traits should increase in frequency that didn’t

Question 21

Questions people had after mendle

Answer 21

1. Why don’t dominant alleles take over populations
2. What will happen to the genotype and allele Frequencies in the next generation

Question 22

Adjusting Punnet Square

A = 0.3
a = 0.7

Answer 22

Can add allele Frequency into punnet square

Freq of AA = 0.3 X 0.3 = 0.09
- Because Frequency of sperm A and Frequency of egg will A combing

Question 23

Finding genotype Frequencies P/Q

Answer 23

P = Freq A
q = Freq of a

Freq of AA = P^2
Freq of Aa = 2pq (P X Q OR Q X P)
Freq of aa = q^2

Question 24

What does H-W show

Answer 24

Shows how Frequencies of dominant allele can stay low

Question 25

H-W example AA = 9 Aa = 42 aa = 49 Show allele and genotype Frequency

Answer 25

Question 26

Adjusting Punnet Square (shematic)

Answer 26

Can add in P and Q

Question 27

P and Q in punnet square

Answer 27

Shows how H-W is derived P and P = P^2 P and Q OR Q and P = 2pq Q and Q = Q^2 Can add in P and Q into punnet square -- show how H-W is derived

Question 28

What does H-W describe

Answer 28

H-W describes allele frequency in population

Question 29

H-W (Details)

Answer 29

Allele frequencies --> Sum of all allele frequencies add to 1 (P + Q = 1.0) Genotype frequencies = dictated by punnet square P^2 + 2pq + q^2 = 1.0 In H-W the allele frequencies don't change over time

Question 30

Assumptions of H-W

Answer 30

Population that allele/genotype frequencies don't change has assumptions 1. No Migrations in or out of population 2. No Mutation 3. No natural Selection (natural or artificial) --> No one genotype is better than the other 4. Random mating 5. Infinite population size

Question 31

What does H-W work for?

Answer 31

P^2 + 2pq + q^2 = 1 --> assumption that only works for organisms that are diploid -- works for diploid

Question 32

Evolution

Answer 32

Change in allele frequency over time

Question 33

What do we get from H-W

Answer 33

Get expected values

Question 34

Why would expected values be different than observed values

Answer 34

If expected don't matched observed values -- need to ask why not --> population must be in violation of one of the assumptions

Question 35

What do allele frequencies reflect in a population

Answer 35

In a population allele frequencies are a reflection of genetic diversity

Question 36

Example -- Is Pleibald spotting likely in H-W --> Do you think that pleiblad spotting with have evolution

Answer 36

Look at all of the assumptions: 1. Is theer selection --> No 2. is there reanodm mating --> Yes there is no difefrnce is mating because of pleibald 3. Is there migration -- No --> no one is leaving because of Pleibald 4. Is there increased or decreased mutations --> No -- Pleibald won't increase or decrease mutations 5. Is there reduced population size because of being pleibald --> NO -- pleibald would not affect popultion size

Question 37

Calculating Expected values Example SS -- 151 Ss -- 131 ss -- 44

Answer 37

Find P and Q from genotype frequncies Once have P and Q can find expected genotype frequencies (P^2 + 2pq + q^2 = 1.0 -- gives genotype frequencies) Multiply expected genotype frequency by total individuals in populations

Question 38

How can we test whether a popultion is under H-W

Answer 38

Do a Chi Square GOF test -- Look at the observed vs. expected values

Question 39

Null Hypothesis

Answer 39

Differences between observed and expected values is due to random chance/sampling error

Question 40

Pleibald Spotting Example SS -- 151 Ss -- 131 ss -- 44

Answer 40

Take observed --> get allele frequencies (find p/q) --> Find expected genotype frequencies

Question 41

Determining Df in H-W

Answer 41

df = # of genotype classes - # of alleles Example: 3 genotype classes (AA + Aa + aa) 2 Alleles df = 3 - 2 = 1 ***We lose an extra degree of freedom because the frequencies of p and q are not independent

Question 42

Answer 42

NO -- because don't know AA or Aa -- can't count a -- don't know allele frequencies Don't know how many are AA or Aa = can't count frequency of a or A alleles IF CAN'T CALCULATE ALLELE FREQUNCIES = CAN'T TEST IF POPULATION IS IN H-W

Question 43

What do you know to test whether a population is in H-W

Answer 43

Allele frequencies mist be known

Question 44

Answer 44

NO -- because don't know allele frequency -- don't know TT vs tt = don't know allele frequency

Question 45

Evolution + PTC

Answer 45

PTC is not found in nature but the ability to taste PTC correlates with the ability to taste other bitter compounds -- there may have been selective advantage for tasters in early evolutionary history - May have helped individuals choose what to eat - Sequence analysis of modern human populations show that TAS alleles are under H-W --> they are no longer being selected for if it is under H-W

Question 46

Answer 46

Question 47

Answer 47

Answer -- 0.2 Allele 1 + Allele 2 + Allele 3 = 1.0 100% of alleles are 1, 2 or 3

Question 48

Answer 48

Because still diploid organism = only one egg and one sperm

Question 49

H-W for more than 2 alleles per locus

Answer 49

Can do H-W with more than two alleles