1. Biology Unit 7 Notes: Evolutionary Mechanisms

2. KEEP IN MIND Evolution is a process of change in living organisms.
“Change” = Change in allele frequencies.
Genetic Variation allows for changes in allele frequencies.
There is no “one way” evolution occurs. Evolution is not changing because you need to/want to, or to make something “better”.
Only the traits present in a population can be passed on.

3. (1) Types of Mechanisms
“Evolution Mechanism”  Something that drives or initiates the change in a population.
The Types:
Genetic Mutations
Genetic Migration
Genetic Drift
Geographic Isolation

4. (2) Organisms Descend with Modification
Organisms have changed, over time, in comparison to their common ancestor.
Common Ancestor?
This is not some mother animal that gave birth to all plants and animals.
It is the first, most primitive life form that existed on this planet.
What has changed?
Gene (Allele) frequency within a population over time.
The alleles which offspring can inherit.

6. (3) The Gene Pool
Every population has a variety of genes that can be inherited.
Gene combinations flow in and out of a population throughout time.
Sex also increases the variety of gene combinations through random assortment.
Differences in individuals  Changes in a population  EVOLUTION

8. (4) Allele Frequency Frequency = How often something shows up.
Allele = Trait
Evolution = Change in the allele frequency within a population.
Crows like to eat green beetles.
The starting population of beetles is 90% green and 10% brown.
Generations pass, the population is now 70% brown and 30% green.

9. (5) Genetic Migration
Movement of organisms between different populations of a species.
As the organisms move, they obviously carry their genes with them.
Organisms with unique traits mate with different population.
New allele combinations are introduced to population.
Migration increases variation  Which increases the chance for change + EVOLUTION!!

10. [Example  You don’t HAVE to copy it.]
Flower Pollen = Flower Sperm
Contains unique traits/alleles
If the pollen of certain flowers is carried by the wind to a different population….
Alleles of one flower population will now combine with alleles of another population
New alleles are introduced
Allelic combinations of offspring could be different  Different phenotypes

13. (6) Genetic Drift Completely random survival of certain traits:
Certain individuals do not find a mate, are killed, or their offspring is killed.
Unfortunately they will not pass on their traits.
This changes the allele frequencies of future generations.
Constantly occurring, and constantly changing populations.
NO relationship to fitness of individuals.

14. [Example  You don’t HAVE to copy it.]
Red spots versus Yellow spots…
Initially population is 80% red spots, 20% yellow spots.
Some of the red spot caterpillars are: Stepped on, Fall off tree, Eaten.
Fewer red spot caterpillars to reproduce.
Eventually population is 60% red spots, 40% yellow spots.

16. (7) Geographic Isolation
Examples of Geographic Barriers:
Forestry
Human Construction
Bodies of Water
Mountains/Hills or Depressions/Canyons
Organisms that used to exchange alleles during reproduction no longer can….
Change in the allele variation available to a population.
The two populations have different mutations, genetic drift, and natural selection events.
Eventually they become reproductively isolated populations  NEW SPECIES (EVOLUTION!!)

19. (8) Speciation
Species: A group of similar organisms that can breed and produce fertile offspring.
Speciation: The production of a new species.
Causes for Speciation:
Loss of physical attractiveness
Change in anatomical parts
Geographic barriers
Migration