1. Evolutionary Mechanisms
Other
Evolutionary Mechanisms
Hawaiian Red jungle fowl exhibit greatly elongated tails, and blonde hackles in many males, another trait accrued from G. Various hybrid founders. 1

2. Genetic Equilibrium Vs. Evolution
In genetic terms, evolution is any change in the relative frequency of alleles in a population.
The situation when the allele frequencies remain the same is called genetic equilibrium.
If the frequencies do not change, the population will not evolve.

3. Maintaining a Species
In order to maintain a species (no new alleles in gene pool), certain criteria must be met.
There must be:
A large population
No change in DNA
No natural selection
No immigration or emigration
Random mating
These 5 conditions are referred to as the
Hardy-Weinberg Principle. 3

4. Population Size Effects
In small populations, there are less options for mating, therefore any evolutionary changes occur more rapidly
In large populations there are more alleles available, so one change does not make a big difference to the population
These changes are due solely to chance factors. The smaller the population, the more susceptible it is to such random changes and loss in genetic variation.

5. If evolution DOES occur, it may be through:
Genetic drift
Bottleneck Effect
Founder Effect
Gene Flow
Mutations
Genetic Recombination

6. Genetic Drift
Genetic Drift is the random change in allele frequencies that occurs in small populations.
Some individuals, just by chance, leave behind a few more descendents than others.
This is different than natural selection because it is not survival of the fittest

7. Genetic Drift
Genetic drift can cause populations to lose genetic variation and it does not usually create new adaptations.
There are two types of genetic drift:
Bottleneck Effect
Founder Effect
See hill.com/sites/ /student_view0/chapter20/simulation_of_genetic_drift.ht ml 7

8. The Bottleneck Effect
Environmental events may reduce population sizes dramatically ex: earthquakes, floods, fires, and over hunting by humans
Those that survive the disaster may not accurately represent the original population
Alleles may be overrepresented among survivors, some may be eliminated completely.

9. The Founder Effect
Occasionally a small group of individuals within a population may migrate and become isolated from the original population.
This smaller group is the ‘founding’ population
The result for this new founding population is often high frequencies of specific genetic traits inherited from the founding ancestor
Certain alleles may go missing all together as a consequence, resulting in a loss of genetic diversity.

10. The Founder Effect
Population
Island
The Mainland

11. The Founder Effect The Mainland
A few individuals colonize a new isolated area
The Mainland 11

12. The Founder Effect
There may be a higher frequency of one allele in the founder population just by chance
This allele did not have been very common in the original population 12

13. The island population grows
The Founder Effect
Island
The island population grows 13

14. …after a few generations
One allele may be lost completely if individuals fail to leave offspring carrying it.
Island 14

15. …after a few generations
Mutations may occur creating new alleles
Island 15

16. …after a few more generations
The new allele becomes more common
Island 16

17. The 2 populations now look very different!
Island
The Mainland 17

18. Remember…. If evolution DOES occur, it may be through:
Genetic drift
Bottleneck Effect
Founder Effect
Gene Flow
Mutations
Genetic Recombination

19. Gene Flow
Gene flow is when alleles are transferred from one population to another. 
This happens when
there is migration.
If alleles are carried to a population where those alleles previously did not exist, gene flow can be a very important source of genetic variation.

20. Gene Flow
By moving alleles around, it can make distant populations genetically similar to one another, thus reducing the chance of speciation.
Example: The allele for brown coloration moves from one population to another and eventually both populations will have brown alleles.

21. Remember…. If evolution DOES occur, it may be through:
Genetic drift
Bottleneck Effect
Founder Effect
Gene Flow
Mutations
Genetic Recombination

22. Mutations Mutations are random changes in DNA.
Mutations can be beneficial, neutral, or harmful for an organism, but mutations do not “try” to supply what the organism “needs.”
To pass a mutation on to the next generation, it must occur to a reproductive cell (gamete).

23. Remember…. If evolution DOES occur, it may be through:
Genetic drift
Bottleneck Effect
Founder Effect
Gene Flow
Mutations
Genetic Recombination

24. Genetic Recombination
Sexually reproducing organisms can create new combinations of alleles.
Crossing-over that occurs in meiosis can recombine or “shuffle” alleles in sex cells.

25. Genetic Recombination
When egg and sperm meet, the offspring inherits a combination of genes that is totally unique.
Gametes carries versions of genes from previous generations plus any mutations that occurred during meiosis

26. Effect of Genetic Recombination
Differences among individuals add to the diversity and variation within the population.
Diversity means that alleles are changing over time, which means that evolution is occurring.

27. In Summary… Changes to a population over time = EVOLUTION
No changes to a population = genetic equilibrium = NO EVOLUTION
The four ways that changes CAN be made to a population are explained above!