1. Evolutionary Change Without Selection
Section 8.1

2. Evolutionary Change without Selection
Learning Goal: To explore causes of evolutionary change that are not influenced by the traits of individuals.
Success Criteria:
I know I am succeeding when I can…
discuss genetic drift, and the consequences of the founder effect and bottlenecks
describe the Hardy-Weinberg principle
explain how human activities affect the evolution of other species
Not all evolutionary changes are result of NS
Sometimes changes in genetic makeup of pop. not influenced by traits of individuals
These changes tend to reduce genetic diversity within pop

3. Genetic Drift
Genetic Drift: changes to allele frequency as a result of chance
more pronounced in small populations
can result in a particular allele becoming either very common or disappearing entirely over a number of generations
lost alleles reduce genetic diversity of the population

4. Bottlenecks and the Founder Effect
Bottleneck Effect: a dramatic, often temporary, reduction in population size, usually resulting in significant genetic drift
Pop of reduced to 50, unlikely to contain all alleles found in larger pop
Many alleles, particularly rare alleles likely to be eliminated
If pop recovers, genetic makeup limited to alleles carried by 50 indiv and any new mutations

5. Bottlenecks and the Founder Effect Cont’d…
adverse consequences for populations
ex. cheetahs
cheetahs are descendants of a population that experienced a severe bottleneck event 10, 000 years ago which left only 7 cheetahs
reduced genetic variability in the population
as a result cheetahs are vulnerable to disease, have low reproductive success and high juvenile mortality rates
Similarly, the northern elephant seal population was reduced by
overhunting to 20 individuals in the 1890s. Although the population has rebounded
to over individuals, they are genetically very similar.

6. Bottlenecks and the Founder Effect Cont’d…
Founder Effect: genetic drift that results when a small number of individuals separate from their original population and establish a new population
new population may begin with a different frequency of alleles
Original pop has allele in 1 of 1000 finches (0.1%)
Suppose by chance, 1 of only 20 finches on new island carry allele
That’s 5%, an increase of 50 times
Doesn’t increase diversity, but new pop begins with different gene pool

7. Hardy–Weinberg principle Hardy–Weinberg principle
Hardy–Weinberg principle: in a stable and non-evolving population, gene frequencies remain the same unless acted upon by evolutionary forces
- mathematically, a gene pool can be described by the frequency of each of the alleles within a pop

8. Hardy–Weinberg principle Hardy–Weinberg principle…
serves as a control in population studies
tells us what to expect if a population is not evolving
If results suggests otherwise, then the population must be evolving, and we can then study the causes such as….
natural selection: favours the passing on of some alleles over others
small population size: increases the likelihood of genetic drift
mutation: introduces new alleles to a population
immigration or emigration: introduces or removes alleles in a population
horizontal gene transfer: the gaining of new alleles from a different species
- Any factor that causes allele frequency to change leads to evolutionary change

9. Consequences of Human Influence
human activities (such as harvesting species, altering habitats and polluting the environment) have a very strong selective influence on many species and therefore influence their evolution
ex. climate change in some cases is happening to rapidly for species to adapt such as with caribou that live in the Artic
*Refer to table on page 334*

10. Evolutionary Change without Selection
Learning Goal: To explore causes of evolutionary change that are not influenced by the traits of individuals.
Success Criteria:
I know I am succeeding when I can…
discuss genetic drift, and the consequences of the founder effect and bottlenecks
describe the Hardy-Weinberg principle
explain how human activities affect the evolution of other species
This lesson will present the many forms of evidence that convinced Darwin that species had changed over time and that species appeared to share a common ancestry. The basis of his theory on the evolution of species.

11. Homework
8.1 questions #9-11, 13 &14