1. Evolution of Populations
Chapter 16

2. Genes and Variation
Relative (allelic) frequency - the percentage of a particular allele in a gene pool.

3. Selection
Natural Selection- In nature, unequal ability to survive and reproduce... Survival of the fittest.
Natural Selection ACTS ON PHENOTYPE but influences genotype (thus, allelic frequency)
Artificial Selection- Mankind selects for desired traits. Also known as “selective breeding”

4. Over time, the zebra herd becomes faster as the slower zebra (and their genes) are removed from the population… survival of the fittest Darwin’s Theory = Evolution by means of natural selection

5. Artificial Selection

6. ADAPT OR DIE!
Camouflage- organisms blend-in with surrounding environment
Mimicry- species copy another to insure their own survival
NatGeo

7. Genes and Variation
Gene pool - all the genes that exist within a population

8. Gene flow – movement of alleles into or out of a population
Immigration – new alleles move IN
Emigration – alleles move OUT

9. Genetic drift - change in allelic frequencies by chance
Ex: sudden extinction of a dominant species; small populations most affected

10. Genetic equilibrium - when alleles stay the same from generation to generation
The Hardy Weinberg Principle: Allele frequencies will remain constant under five conditions
Random Mating
Large Population
No movement (immigration or emigration)
No Mutations
No Natural Selection: equal change of survival

11. Hardy-Weinberg Equation
(p + q)2 = 1, which is the same as
p2 + 2pq + q2 = 1
p = frequency of “A” allele and
q = frequency of “a” allele
p2 = expected freq. of homozygotes for one allele
2pq = expected freq. of heterozygotes
q2 = expected freq. of homozygotes for the other allele

14. Natural Selection effects Genetic Change in Populations
Natural Selection has three affects on phenotype distribution
Directional Selection
Stabilizing Selection
Disruptive Selection

15. Directional Selection
Directional Selection- Individuals on one end of a curve are “better fitted” than the middle or other end
Peccaries naturally choose to consume those
cactus plants with the fewest spines As a result,
at flowering time there are more cacti with
higher spine numbers; thus, there are more of
their alleles going into pollen, eggs, and seeds
for the next generation.

16. Stabilizing Selection
Stabilizing Selection- Individuals near center of a curve are “better fitted” (have highest fitness) than both ends
Peccaries are consuming the low-spine
number plants, and the insects are killing
the high-spine-number plants. As these
gene combinations are removed from the
cactus gene pool, there is less and less
variety possible in subsequent
generations.

17. Disruptive Selection
Disruptive Selection- Individuals at upper and lower ends are “better fitted” than the ones in the middle
Years of collecting have left their toll on
the roadside cacti. In this environment, it is
maladaptive to be good looking and have
a reasonable number of spines. Low
spine-number plants are not picked
because they don't "look right", and high
spine-number varieties are left alone
because they are too hard to pick.
Gradually, the gene pool changes in favor
of the two extreme spine number types.

19. Patterns of Evolution Extinction
Divergent Evolution (adaptive radiation)
Convergent Evolution
Coevolution

20. Extinction
Why do species go extinct?

21. Extinction
Natural selection, climate changes, and catastrophic events have caused 99 percent of all species that have ever lived to become extinct.
Mass extinctions – caused by continents moving, sea level changing, volcano eruptions, large meteors

22. Predict what each ecosystem will look like after the event.
Catastrophic
Event
Catastrophic
Event

23. Question
When a mass extinction happens, what do you think will happen next?

24. Divergent Evolution (adaptive radiation)
Divergent evolution – natural selection causes 1 species to evolve into many species with many different adaptations (homologous structures)
After mass extinctions, many environments will be open for inhabitation
Species will migrate to that area and new environmental pressures will cause the population to change over time
This is also known as Adaptive Radiation

25. Adaptive Radiation in honeycreepers

26. Convergent Evolution
Convergent Evolution – when unrelated organisms come to resemble one another (analagous structures)

27. Coevolution
When 2 species evolve in response to one another

28. ---DIVERGENT EVOLUTION---
Evidence of Evolution
Homologous structures - similar structures found in related organisms that are adapted for different purposes.
Ex: human arm and bat wing or whale flipper
---DIVERGENT EVOLUTION---
the process of two or more related species becoming more and more dissimilar.

29. Homologous structures  Divergent evolution

30. ---CONVERGENT EVOLUTION---
Analogous structures - structures found in unrelated organisms that have a similar function but may be structurally different
Ex: bird wing and insect wing
---CONVERGENT EVOLUTION---
independent evolution of similar features in species of different lineages

31. Analogous structures  Convergent evolution

34. Process of Speciation speciation - evolution of a new species
4 Main Isolating Mechanisms
Reproductive
Behavioral
Geographic
Temporal

35. A. Reproductive Isolation: Two populations
A. Reproductive Isolation: Two populations cannot interbred and produce fertile offspring
B. Behavioral Isolation: Two populations capable of breeding but cannot because of courtship rituals

36. C. Geographic Isolation: Two populations are separated by geographic barriers
Ex: Rivers, Oceans, Mountains
D. Temporal Isolation: Two or more populations reproduce at different times

37. Genes and Variation Sources of genetic variation:
Mutations- change in DNA sequence
Gene Shuffling- random assortment of genes during gamete production (SEXUAL reproduction)
Gene Expression Variation
Single-gene trait- controlled by one gene
Ex: Widow’s Peak
Polygenic trait- controlled by many genes
Skin color, eye color

38. Original Source of Genetic Variation?
MUTATION!
the evolution of sexual reproduction increased genetic diversity within a population and therefore accelerated the rate of evolution