1. Evolutionary Change Without Natural Selection

2. Evolution occurs when natural selection acts on the genetic variability within populations.
Genetic variation occurs by chance through genetic mutations and recombination.
BUT, natural selection does NOT occur by chance – the environment favours certain individuals over others.

3. Evolutionary Change without Selection
Sometimes change in the genetic makeup of a population is not influenced by the traits of individuals.
Genetic Drift

4. Genetic Drift
When the genetic makeup of a population changes by chance.
The chances of passing on any particular allele is random
Therefore, it is possible for one allele to occur more frequently than another, without the allele being naturally selected for

5. Activity
If you flip a coin 10 times, what should your expected results be?
Do it! Did you get the expected 1:1 ratio.
Would your results be closer to the expected probability if you flipped the coin 100 times?

6. Genetic Drift
The smaller the number of individuals in a population the greater the influence of genetic drift.
As a result, alleles can completely disappear over a number of generations.
The loss of an allele means a reduction in genetic diversity.

7. Bottleneck and Founder Effect
If a population were to undergo an extreme reduction in size, this would lead to a loss of genetic diversity and what is known as a bottleneck.
A population bottleneck may be the result of genetic drift or natural selection. Which one do you think plays a bigger role?

9. Bottleneck
Ex: If initially a population contained individuals, there is likely lots of different alleles and variation in this population.
If the population drops to 50 individuals, many of those alleles will be lost.
If the population is allowed to recover, those 50 individuals are the “founders” of the new population. (FOUNDER EFFECT)

10. Founder Effect
Future generations will only have the alleles that were present in the founder and there will be a lack of genetic diversity in the resulting populations.

11. Cheetahs are an example of a species that has undergone a population bottleneck and a founder effect.

12. Why is lack of Diversity bad?
Lack of diversity makes a population susceptible to diseases and catastrophic events.
Essentially inbreeding, which leads to the expression of harmful homozygous recessive traits that are usually rare and not expressed.
Can lead to the extinction of a species.

13. Diversity and the Founder’s Effect
Populations under the founder effect will demonstrate a lack of genetic diversity in the years that follow the population bottleneck and will be vulnerable for extinction.
With time, after several generations, mutations will build up in the gene pool and genetic diversity will increase.

15. Evolution
Natural Selection