The Founder Effect

The Founder Effect: Occurs when a small number of individuals from a population found a new population that is reproductively isolated from the original one. It is a special case of Genetic Drift and can be seen in the Amish populations of the United States - they have grown from a very few founders, have not recruited newcomers and tend to marry within the community.

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Example: Spotted=ss, Non-Spotted=SS or Ss

The New Population Is Made Up Of Spotted Giraffes, All With The Recessive Allele,
 Making Them Unable To Have Non-Spotted Offspring

A Smaller Gene Pool And Allele Frequency Is The Result

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The effect of Genetic Drift is inversely related to population size:

Large Population = Small Effect - Little change in allele frequency.

Small Population = Large Effect - Dramatic change in allele frequency.

The Bottleneck Effect

The Bottleneck Effect: The allele frequency in the population is altered due to a catastrophic event.

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Example: Orange=YY, Yellow=Yy, Green=yy

3:3:1

A Happy Colony Of Giraffes

Then Suddenly... A FIRE COMES

2:1:0

Only A Small Number Of Giraffes Survive

The Dominant Allele is More Common (Y:y = 5:1)

Genetic Drift

Genetic Drift: Random change in allele frequency causes an allele to become more common or less common.

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Example: T=Tall, t=Short (T:t)

5:7

Only The Three Circled Giraffes Leave Offspring

5:5

Only The Two Circled Giraffes Leave Offspring

10:0

Now The Only Allele Present Is The Tall (T) Allele

Gene Pool and Allele Frequency

Gene Pool: The total variety of genes and alleles present within a population at a given point in time.

Allele Frequency: How common an allele is in a population (e.g. B:b = 10:6).

Example:

Gene Pool = Only Short-Necked Giraffes

A New Long-Necked Comes Along (Immigration)

He Adds New Genes/Alleles To The Gene Pool

Now The Giraffes Can Reach The Trees

Yay!

EVOLUTION

...Or They Would've Turned Into Cows

This evolution would increase the population of giraffes because there is more food for them to eat (tree leaves) and less competition with other animals for grass.

Evolution Glossary

Common words and their definitions:

Gene - A Segment of DNA that determines our characteristics.

Allele - Different forms of a gene.

Species - Individuals that interbreed to produce fertile offspring.

Population - A group of individuals of the same species living in the same area.

Gene Pool - The total variety of genes and alleles present within a population at a given point in time.

Gene Flow - The transfer of alleles of genes from one population to another.

Allele Frequency - How common an allele is in a population.

Immigration - New individuals added to the population bringing new alleles into the gene pool.

Emigration - Individuals leave a population, taking away some alleles from the gene pool.

Evolution - Change in the gene pool of a population over a period of time.