Topic 7: Gene Flow

Question 1

What is genetic differentiation?

Answer 1

• 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

Question 2

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

Answer 2

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

Question 3

What is a ‘Metapopulation”

Answer 3

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

Question 4

Without gene flow, two subpopulations will become….

Answer 4

genetically differentiated

Question 5

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

Answer 5

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

Question 6

What is gene flow?

Answer 6

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

Question 7

With high gene flow, two subpopulations ….

Answer 7

will remain homogenous, and genetic differentiation will not occur

Question 8

What are the two major evolutionary impacts of gene flow?

Answer 8

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

Question 9

If gene flow is constant, eventually __________will be reached…

Answer 9

EQUILIBRIUM

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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.

Question 12

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

Answer 12

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

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

Question 13

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

Answer 13

MIGRATION RATE

Question 14

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

Answer 14

sewall wright

Question 15

What are wrights f-statistics?

Answer 15

• 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

Question 16

What does Wright’s F-statistics describe?

Answer 16

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)

Question 17

What are the 3 f-statistics?

Answer 17

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

Question 18

Fst is a ….

Answer 18

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

Question 19

What is the equation for Fst?

Answer 19

Fst = Ht - Hs / Ht

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

Question 20

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

Answer 20

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

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

Question 21

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

Answer 21

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

Question 22

Genetic drift increases _____, and gene flow decreases ______

Answer 22

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

Question 23

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

Answer 23

Fst

Question 24

What is the Wahlund Effect?

Answer 24

• 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

Question 25

What is admixture?

Answer 25

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

Question 26

What are the benefits of admixture? Drawbacks?

Answer 26

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