1. Mechanisms of Evolution

2. Evolution Changes in a population over time.
Mechanisms of evolution (8)
Mutations
Gene flow
Genetic drift
Natural Selection (survival of the “fittest”)
Artificial Selection
Recombination
Non-Random Mating
Isolations (speciation)

3. Mutations
Mutations are random changes in DNA, which if favorable, can be passed down from one generation to the next.
These random mutations play an important role in evolution

4. Mechanism of Evolution: Mutations
Original Population

5. Mechanism of Evolution: Mutations
After Mutation

6. Mechanism of Evolution: Mutations
Many Generations Later
Make sure students compare the original population to the population many generations later. This will help them see how the population changed as a result of the mutation.

8. Gene Flow
Genes move with individuals when they move (emigrate or immigrate) into and out of a population…and it changes the gene pool

9. Genetic Drift
Genetic Drift – the random fluctuation due to chance occurrences alone
It is more significant in smaller populations
It increases the chance of any given allele becoming more or less prevalent when the number of individuals is small
Ex.) Founder Effect and Bottleneck Effect

10. Section 15.1 Summary – pages 393-403
Natural Selection
Natural selection is the idea that organisms with favorable/beneficial traits survive, reproduce, and pass those traits to the next generation “Survival of the Fittest”.
ENVIRONMENTALLY CONTROLLED
Organisms without these variations/traits are less likely to survive and reproduce.
Section 15.1 Summary – pages

11. Section 15.2 Summary– pages 404-413
NATURAL SELECTION
There are three different types of natural selection: stabilizing, directional, and disruptive.
Stabilizing selection is a natural selection that favors average individuals in a population.
Evolution will not occur
Middle sized Siberian Huskies are selected for
Section 15.2 Summary– pages

12. Section 15.2 Summary– pages 404-413
NATURAL SELECTION
Directional selection occurs when natural selection favors one of the extreme variations of a trait.
This type of selection can lead to rapid evolution of a population.
Section 15.2 Summary– pages

13. Section 15.2 Summary– pages 404-413
NATURAL SELECTION
In disruptive selection, individuals with either extreme of a trait’s variation are selected for.
This results in eventually having no intermediate form of a trait, and leading to two separate species.
Section 15.2 Summary– pages

14. Natural Selection
Shifts to
middle range
2 extremes
1 extreme

15. Section 15.1 Summary – pages 393-403
ARTIFICIAL SELECTION
Breeding organisms with specific traits in order to produce offspring with ideal (Intentional breeding for certain traits)
A Goldendoodle
(Golden retriever/ Poodle)
Section 15.1 Summary – pages

16. Recombination (Crossing over)
As we learned in the genetics unit, CROSSING OVER leads to genetic material being shuffled.
This shuffling, along with sexual reproduction, leads to variation within populations. This variation leads to selection, which ultimately leads to evolution.
Locate an appropriate website or websites with real world examples of recombination and genetic shuffling. Possible websites to consider are the Berkeley Evolution website and the Learn Genetics Utah website. These online libraries have many resources which you may find appropriate for your students and district. Embed examples onto this slide.

17. The red coated birds traits are favored in choosing a mate
Non-Random Mating
Blue = BB or Bb
Red = bb
Original Population
The red coated birds traits are favored in choosing a mate x
Students may need to think about Punnett squares probability of offspring. It maybe helpful to do a cross between two heterozygotes and also two red individuals. This will show students that not only are red individuals all red offspring but blue individuals are also producing red offspring as well. Because of this and non-random mating, the frequency of red alleles will increase many generations later.
Most species do not just mate randomly… there are desired or favorable traits that they look for when choosing a mate (ex..peacocks)

18. Many Generations Later
Non-Random Mating
Over time, you would see the favored traits more prevalent than the undesired traits.
Many Generations Later

19. Reproductive Isolation
Two ways reproductive isolation occur:
Prezygotic mechanisms
Geographic
Temporal
Mechanical
Behavioral
Postzygotic mechanisms
Infertility

20. Section 15.2 Summary– pages 404-413
SPECIATION
The evolution of new species, a process called speciation.
This occurs when members of similar populations change so much from each other that they no longer interbreed to produce fertile offspring.
Section 15.2 Summary– pages

21. Section 15.2 Summary– pages 404-413
SPECIATION
In nature, physical barriers can break large populations into smaller ones.
Geographic isolation occurs whenever a physical barrier divides a population and over time they change and become two different species.
Reproductive isolation…
Section 15.2 Summary– pages

22. Section 15.2 Summary– pages 404-413
SPECIATION without a physical barrier
Some speciation occurs while the organisms still exist in the same area…
Reproductive Isolation
Behavioral, Temporal, Mechanical
Section 15.2 Summary– pages

23. Speciation Northern Arctic Fox Spreads northward and
Adapted to heat
through lightweight
fur and long ears,
legs, and nose, which
give off more heat.
Adapted to cold
through heavier
fur, short ears,
short legs, short
nose. White fur
matches snow
for camouflage.
Gray Fox
Arctic Fox
Different environmental
conditions lead to different
selective pressures and evolution
into two different species.
Spreads
northward
and
southward
separates
Southern
population
Northern
Early fox