Topic 7: Gene Flow Flashcards

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1
Q

What is genetic differentiation?

A
  • How a singular population may be composed of geographic subpopulations, and these distinct clusters often have different genetic frequencies from one another
  • differences in genetic variation among subpopulations
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2
Q

Is genetic variation distributed uniformly across the range of a species/population?

A
  • Rarely.
  • most often, a species range is composed of geographic subpopulations, which have different levels of genetic variation
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3
Q

What is a ‘Metapopulation”

A
  • a “population of populations”
  • refers to the larger population that contains subpopulations
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4
Q

Without gene flow, two subpopulations will become….

A

genetically differentiated

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5
Q

The _________ two populations are isolated, or the _______ migrants they exchange, the ______ genetically differentiated they will become overtime

A

The LONGER two populations are isolated, or the FEWER migrants they exchange, the MORE genetically differentiated they will become overtime

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6
Q

What is gene flow?

A
  • the movement of individuals between subpopulations that results in genetic exchange
  • tries to ensure that two subpopulations will not become genetically differentiated
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7
Q

With high gene flow, two subpopulations ….

A

will remain homogenous, and genetic differentiation will not occur

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8
Q

What are the two major evolutionary impacts of gene flow?

A
  • introduction of new alleles to a population, changes frequency of alleles
  • reduce genetic differences between populations (homogenize subpopulations
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9
Q

If gene flow is constant, eventually __________will be reached…

A

EQUILIBRIUM

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10
Q

What are the 4 models of gene flow? explain them all

A
  1. continent - island
    - unidirectional, one way movement of individuals from continent to island
  2. Island model
    - equal exchange of individuals between all islands
  3. stepping stone
    - migration only occurs between adjacent populations
  4. 2D stepping stone
    - grid, but migration still only occurs between adjacent populations
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11
Q

What is the general equation for calculating the change in allele frequency over time for a continent-island gene flow model?

A

Pt = (1-m)^t (P0 - P) +P

(1-migration rate) x (allele f. of island at time 0 - allele f on continent) + allele f. on continent.

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12
Q

What is the equation for two way gene-flow, to estimate change in allele frequency?

A

Pa t+1 = (1-m)Pa t + mPb t

(1- migration rate) x (frequency in population a) + (migration rate x frequency in population b)

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13
Q

How quickly two subpopulations will reach equilibrium is dependent on ______ ______

A

MIGRATION RATE

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14
Q

F-statistics (fixation index) was developed by….

A

sewall wright

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15
Q

What are wrights f-statistics?

A
  • a mathematical approach to partition genetic variation in a subdivided population, according to total population, subpopulation, and individuals
  • determining a way to measure genetic differentiation over subpopulations based on deviations from HW
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16
Q

What does Wright’s F-statistics describe?

A

the reduction in heterozygosity from that expected with random mating at one level of hierarchy relative to that expected at a higher level of hierarchy (like subpopulation to entire population)

17
Q

What are the 3 f-statistics?

A
  • Fst: The subpopulation relative to the total population
  • Fis: an individual relative to its subpopulation
  • Fit: individual relative to the total population
18
Q

Fst is a ….

A

measure of genetic variation between subpopulations, relative to the total variation

19
Q

What is the equation for Fst?

A

Fst = Ht - Hs / Ht

Ht= total heterozygotes in population
Hs = total heterozygotes in subpopulation

20
Q

An Fst =1 tells us …. while an Fst of 0 tells us…

A

Fst=1 –> Two subpopulations are completely different, there is no shared variation

Fst=0 –> Two subpopulations have exact frequencies, equal variance.

21
Q

Fis and Fit range from __ to ___, and these values tell us…

A
  • range from -1 - 1
  • positive vales mean less heterozygosity observed, suggesting inbreeding
  • negative means more heterozygosity than expected, which suggests outbreeding
22
Q

Genetic drift increases _____, and gene flow decreases ______

A

Genetic drift increases Fst, and gene flow decreases Fst, where Fst is the genetic differentiation

23
Q

With a larger migration rate, we will have a smaller ….

A

Fst

24
Q

What is the Wahlund Effect?

A
  • the perceived deficiency of heterozygotes due to treating two subpopulations as one
  • two separate subpopulations thought of as one, we see an excess of homozygosity from the data collected
25
Q

What is admixture?

A
  • gene flow between previously separated populations
  • also called ‘hybridization’
26
Q

What are the benefits of admixture? Drawbacks?

A

Benefits:
- relieves inbreeding by adding genetic variation
- introduces adaptive alleles
- may produce hybrid speciation

Drawbacks:
- may cause outbreeding depression, where other genes brought into a new environment may not be as adapted to that environment
- causes genetic homogeneity