Transcript Studying evolution in small populations

Studying evolution in
small populations
Life is a fine balance between
shared commonalities and
amazing diversity.
Factors that cause Changes in
allele frequency
 1.
Natural Selection
 2. Gene Flow
 3. Mutations
 4.
Genetic Drift(affects only small
populations
Genetic Drift
 Changes


Random chance
Shifts allele frequencies
 Chance

that happen to small populations
only affects small populations
Ex. Think about tossing a coin ten times
• First trial 3 heads: 7 tails
• 2nd trial 6 heads: 4 tails
• 3rd trial 5 heads: 5 tails
Imagine the start of a new
population


Imagine a small group
migrates to a new
area
Start new population
 New populations are
usually very small to
begin with
Founder effect

Any influences that affect the new population
 Few organisms start population

Different from mainland where they migrated from
Example

The nene goose



Descendants of the
Canada goose
Less webbed toes,
sharper to climb lava
Rarely need to fly

1778, around 25,000
nene geese left
 Down to 30 by 1950
 Now there are 500
Sound
http://www.nfwf.org/nenegoose.jpg
Inbreeding
 In
small populations, individuals tend to
start to become too similar
 No choice but to mate with close relatives
 Loss of genetic variation
 If only 2 individuals per generation,

Comletely homozygous after only 20
generations
Reason for Inbreeding

Populations can hit a
bottleneck


a drastic reduction in
number
Ex. American bison
http://www.anselm.edu/homepage/jpitocch/genbios/23-05-BottleneckEffect-L.gif


Severe population
bottleneck in 19th
century
Because of hunting
http://www.canadianbiodiversity.mcgill.ca/data/sppphotos/mammals/bison.jpg
Inbreeding depression
 Bad


Effects of Inbreeding
Existence of harmful recessive alleles
Inbreeding increases homozygosity
 Reduced
fertility and survival compared to
large populations
Zoos

Have very small populations of
animals




Set up to preserve animals
Promote awareness of animals
Are prone to inbreeding
Breeders often arrange matings
between distantly related
animals
http://www.darwinfoundation.org/terrest/images/5110_two-penguins.jpg