Founder Effect

							Genetic Drift

 Tyson Adams
 Tyler Stewart
  Steve Peper
                  Genetic Drift
• What is Genetic Drift?
   – Change in allele frequency due to the chance of
     random sampling error
   – A cause of Evolution
• What factors play a role in Genetic Drift?
   – Population size
   – Chance
• How does it effect a population?
   – Can lead to a fixation of an allele
   – The changes caused by drift can be neutral, beneficial,
     or harmful
               Founder Effect
• Small population that have moved or been
  moved to new location (founded)
• By chance allele frequencies in new
  population are likely to be different than
  source population
• Due to sampling error
  – Example. (35 alleles on single locus for lizards and
    15 individuals are founded, the chance is very low
    that they will contain all of the 35 alleles)
                  Silvereyes
• Australia and Tasmania
  – Tasmania to South Island in 1830
  – South Island to Chatham and Palmerston in 1856
  – Palmerston to Auckland in 1865
  – Auckland to Norfolk Island in 1904
• Blood samples from 7 groups
• Genotypes from 6 loci to compare groups
 Which would you expect to have the
      most alleles in common?
A.   Tasmania and Auckland
B.   South Island and Norfolk Island
C.   Chatham Island and Palmerston North
D.   Tasmania and Norfolk Island
E.   Palmerston North and Norfolk Island
           Human Populations
• Pingelapese People
  – 20 survivors from typhoon
  – Heterozygous carrier of a recessive loss-of-
    function allele
  – Achromatopsia (complete color blindness,
    sensitivity to light, poor visual acuity)
  – Usually affects 1/20,000
  – 1/20 on island
 Fixation of Alleles and Heterozygosity
• Activity for Fixation

• What is heterozigosity?

• As alleles drift to fixation or loss, the
  frequency of the heterozygotes in the
  population declines
              Bottlenecking
• Occurs when population is reduced to a small
  size for a short period of time
• Only rare alleles are lost
• What will this do to Genetic Variation?
Bottleneck Example
     What’s the difference between
   founder effect and bottlenecking?
• Founder Effect
  – Small group leaves to new environment
  – More extinctions, changes and stress
  – Need more time to adapt
• Bottlenecking
  – Stay in same place
  – Due to sudden decrease in population size
  – Well adapted and bounce back faster
PopGen Lab
In general what happens to allele frequencies and genotype
frequencies in a small population?

A)   Fixation
B)   They stay the same
C)   They promote heterozygosity
D)   There is a loss of heterozygosity
E)   Both A & D
Heterozygosity in a finite population is lost.


A) True
B) False
What effect does heterozygosity have on a population?


A)   Increases a population’s ability to adapt
B)   Loss of genetic variation
C)   Decreases a population’s ability to adapt
D)   Heterozygosity has no effect on a population
 What is the effect of population size
        on genetic variation?
A. Larger population causes more variation
B. Smaller population causes more variation
C. Variation doesn’t depend on population size
 What is meant by fixation of alleles?
A. All allele frequencies are fixed and will not
   change from generation to generation
B. Allele frequencies drift between 0 and 1.0
C. Once allele frequency reaches 0 it is lost
   forever and if it reaches 1.0 it is fixed
D. B and C
     Which apply to founder effect?
1.   More adaption time
2.   Stay in same place (not relocated)
3.   High stress and changes
4.   Decrease in population size
5.   Recover faster than in bottlenecking

     A.   1,3,4
     B.   1&2
     C.   1,2,3,4,5
     D.   3,4,5