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BIOL332 > Population Genetics > Flashcards

Population Genetics Flashcards

1
Q

Overall Population Genetics

A

All about Frequency – Frequency of alleles + Frequency of genotypes

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2
Q

Why is it important to know Frequency (Ex)

A

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

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3
Q

Example – calculating Genotype Frequency

RR = 1
Rr = 3
rr = 6

A
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4
Q

Sum of all genotype Frequency

A

1.0 – sum of all Frequency should add up to 1.0

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5
Q

Example – calculating Allele Frequency

RR = 1
Rr = 3
rr = 6

A
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6
Q

Calculating Allele Frequency (Overall)

A

Allele/Total # of alleles in population

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7
Q

Sum of all allele Frequency

A

1.0 – sum of all allele = 1

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8
Q

Crash Course Video

A

Look at notes

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9
Q

H-W (Overall)

A

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

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10
Q

What does H-W show?

A

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

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11
Q

Allele frequency change in H-W

A

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

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12
Q

Requirements for H-W

A
  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
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13
Q

H- W equation

A

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

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14
Q

Deriving H-W

A

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

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15
Q

What does H-W show

A

Can see mendle’s laws ay work in a population

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16
Q

What happens if frequencies don’t like up with equilibrium

A

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

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17
Q

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

A

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

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18
Q

History

A

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

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19
Q

Issue Punnet had

A

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

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20
Q

Why did people push against Mendle

A

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

21
Q

Questions people had after mendle

A
  1. Why don’t dominant alleles take over populations
  2. What will happen to the genotype and allele Frequencies in the next generation
22
Q

Adjusting Punnet Square

A = 0.3
a = 0.7

A

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

23
Q

Finding genotype Frequencies P/Q

A

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

24
Q

What does H-W show

A

Shows how Frequencies of dominant allele can stay low

25
Q

H-W example

AA = 9
Aa = 42
aa = 49

Show allele and genotype Frequency

A
26
Q

Adjusting Punnet Square (shematic)

A

Can add in P and Q

27
Q

P and Q in punnet square

A

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

28
Q

What does H-W describe

A

H-W describes allele frequency in population

29
Q

H-W (Details)

A

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

30
Q

Assumptions of H-W

A

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
31
Q

What does H-W work for?

A

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

32
Q

Evolution

A

Change in allele frequency over time

33
Q

What do we get from H-W

A

Get expected values

34
Q

Why would expected values be different than observed values

A

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

35
Q

What do allele frequencies reflect in a population

A

In a population allele frequencies are a reflection of genetic diversity

36
Q

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

A

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

37
Q

Calculating Expected values Example

SS – 151
Ss – 131
ss – 44

A

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

38
Q

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

A

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

39
Q

Null Hypothesis

A

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

40
Q

Pleibald Spotting Example

SS – 151
Ss – 131
ss – 44

A

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

41
Q

Determining Df in H-W

A

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

42
Q
A

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

43
Q

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

A

Allele frequencies mist be known

44
Q
A

NO – because don’t know allele frequency – don’t know TT vs tt = don’t know allele frequency

45
Q

Evolution + PTC

A

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

46
Q
A
47
Q
A

Answer – 0.2

Allele 1 + Allele 2 + Allele 3 = 1.0

100% of alleles are 1, 2 or 3

48
Q
A

Because still diploid organism = only one egg and one sperm

49
Q

H-W for more than 2 alleles per locus

A

Can do H-W with more than two alleles

BIOL332 (25 decks)

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