1. Genetic Variation Within a Population
Population: A group of organisms, all of the same species, which interbreed and live in the same place at the same time.
A population shares a common gene pool.

2. Genetic variation in a population increases the chance that some individuals will survive.
Genetic variation leads to phenotypic variation.
Phenotypic variation is necessary for natural selection.
Genetic variation is stored in a population’s gene pool.

3. Allele frequencies measure genetic variation
Genetic variation is how common is allele in population.

4. Figure 16–2 Relative Frequencies of Alleles
Section 16-1
Sample Population
Frequency of Alleles
allele for brown fur
allele for black fur
48% heterozygous black
16% homozygous black
36% homozygous brown

5. Sources of Genetic Variation
Mutations = any change in a sequence of DNA
Remember: mutations result as a mistake during replication or toxin (chemicals/radiation)
Some mutations effect phenotypes (physical characteristics), which can effect an organism’s fitness (ability to survive)
Gene shuffling = different gene combinations inherited during gamete production creating different genotypes (genetic makeup), different phenotypes and more variation
Crossing over increases number of different genotypes
Does not change the relative frequency of alleles in a population
Think of a deck of cards – there are many possible combinations, but frequency remains same

6. Single-Gene vs. Polygenic Traits
The number of phenotypes produced for a given trait depends on how many genes control the trait.
If it is a trait controlled by a single-gene with 2 alleles, there will be only 2 phenotypes.
Phenotypes of a single-gene is represented by a bar graph
If it is a trait is polygenic with 2 or more alleles, there will be many genotypes and even more phenotypes.
Phenotypes of a polygenic trait is represented by a normal distribution (bell curve)
Frequency of Phenotype
(%)
Phenotype
Frequency of Phenotype
Phenotype (height)

7. Evolution as Genetic Change
Natural selection acts on phenotypes, survival and reproduction determine which alleles are inherited, changing relative frequencies of alleles in a population over time.
Thus evolution is any change in the relative frequencies of alleles in a population’s gene pool and acts on populations, not individuals.

8. Natural selection acts on distributions of traits.
A normal distribution graphs as a bell-shaped curve.
highest frequency near mean value
frequencies decrease toward each extreme value
Traits have a normal distribution when not undergoing natural selection.
Example: human height.

9. Microevolution is evolution within a population.
observable change in the allele frequencies
can result from natural selection
As this map1 shows, sparrows in colder places are now generally larger than sparrows in warmer locales. Since these differences are probably genetically based, they almost certainly represent microevolutionary change: populations descended from the same ancestral population have different gene frequencies.

10. Natural selection can change the distribution of a trait in one of three ways or paths.
Directional selection favors phenotypes at one extreme.

11. Natural selection can take one of three paths.
Stabilizing selection favors the intermediate phenotype.

12. Natural selection can take one of three paths.
Disruptive selection favors both extreme phenotypes.

13. Types of Selection
Designate the colors of the two generations on your note sheet.

14. Gene flow is the movement of alleles between populations.
Gene flow occurs when individuals join new populations and reproduce in new population.
Lots of gene flow results in genetically similar populations.
Limited gene flow results in genetically different populations.
Gene flow in beetles
Gene flow
(wind
movement)
in plants

15. Genetic drift is a change in allele frequencies due to chance.
It is most common in small populations. Genetic diversity can increase or decrease.
A population bottleneck can lead to genetic drift.
The bottleneck effect is genetic drift that occurs after an event drastically reduces population size.

16. Genetic Drift Section 16-2 Sample of Original Population Descendants
Founding Population A
Founding Population B

17. Genetic Drift Section 16-2 Sample of Original Population Descendants
Founding Population A
Founding Population B

18. Genetic Drift Section 16-2 Sample of Original Population Descendants
Founding Population A
Founding Population B

19. The Founder Effect is when a few individuals migrate and start a new population. Due to chance only.

20. Genetic drift has negative effects on a population.
Loses genetic variation preventing some from adapting
Harmful alleles can become more common due to chance alone
Ex: Amish population has higher incidence of Ellis-van Creveld syndrome (form of dwarfism
involving:
short stature, polydactyly (extra fingers or toes), abnormalities of the nails and teeth, and occasionally a hole between the two upper chambers of the heart.

21. Camouflage
Natural selection that favors either blending in with the specie’s natural environment to hide, confuse or distract predators.
Can include: special appendages, coloration and the ability to change color to blend with surroundings as needed.

22. Mimicry
2 basic types:
natural selection favoring coloration to imitate toxic/dangerous species.
Natural selection creating a body part that can mimic another object to increase survival

23. Sexual selection occurs when certain traits increase mating success and become more common.
Females prefer males with
certain traits which become exaggerated in
each generation
males produce many sperm continuously
females are more limited in potential offspring each cycle

24. There are two types of sexual selection.
intrasexual selection: competition among males
intersexual selection: males display certain traits to attract females

25. Hardy-Weinberg equilibrium describes populations that are not evolving.
Used as a model to compare with real data.
Tests factors leading to evolution.

26. Genotype frequencies stay the same if five conditions are met.
Hardy-Weinberg equilibrium describes populations that are not evolving.
Genotype frequencies stay the same if five conditions are met.
very large population: no genetic drift
no emigration or immigration: no gene flow
no mutations: no new alleles added to gene pool
random mating: no sexual selection
no natural selection: all traits aid equally in survival

27. Hardy-Weinberg equilibrium describes populations that are not evolving.
Real populations rarely meet all five conditions.
Real population data is compared to a model.
Models are used to studying how populations evolve.

28. The Hardy-Weinberg equation is used to predict genotype frequencies in a population.
used for traits in simple dominant-recessive systems
p2 + 2pq + q2 = 1
What it means:
p is dominant allele q is recessive allele

29. There are five factors that can lead to evolution.
Genetic drift changes allele frequencies due to chance alone.
Gene flow moves alleles from one population to another.
Mutations produce the genetic variation needed for evolution.
Sexual selection selects for traits that improve mating success.
Natural selection selects for traits advantageous for survival.

30. In nature, populations evolve.
expected in all populations most of the time
respond to changing environments

31. Speciation Speciation = formation of new species
Species = group of organisms that breed with one another and produce fertile offspring (share a common gene pool)
As new species evolve, populations become reproductively isolated from each other: When 2 populations can’t breed and produce fertile offspring, resulting in separate gene pools
Behavioral isolation: Capable of breeding, but have different courtship rituals or behaviors
Geographic isolation: Separate by geographic barriers
Temporal isolation: Reproduce at different times

32. Speciation of Darwin’s Finches
Speciation in the Galapagos finches occurred by:
Founding a new population: A small population of finches migrates to a different island
Geographic isolation: Finches don’t usually fly over open water, so stayed on own island (separate gene pool)
Changes in the new population’s gene pool: Adapted to new environment (directional selection) to be more fit
Reproductive isolation: Differences in phenotypes and mating rituals may turn different finches off to one another
Ecological competition: Similar finches compete, so individuals that are most different from each other have the highest fitness, because less competition.
Continued Evolution: Process repeats and over many generations, it produced the 13 different finch species

34. Evolution through natural selection is not random.
Natural selection can have direction.
The effects of natural selection add up over time.

35. Convergent evolution describes unrelated species becoming similar due to common environment.
Ex. Dolphins, sharks and penguins

36. Divergent evolution describes close related species become dissimilar.
How do convergent and divergent evolution illustrate the directional nature of natural selection?
ancestor
Kit fox
Red fox

37. Species can shape each other over time.
Two or more species can evolve together through co-evolution.
evolutionary paths become connected
species evolve in response to changes in each other

38. Coevolution can occur in beneficial relationships.
Both species benefit
Ex. Ant and acacia plant

39. Co-evolution can occur in competitive relationships, sometimes called evolutionary arms race.

40. Species can become extinct.
Extinction is the elimination of a species from Earth.
Background extinctions occur continuously at a very low rate.
occur at roughly the same rate as speciation
usually affects a few species in a small area
caused by local changes in environment

41. Mass extinctions are rare but much more intense.
destroy many species at global level
thought to be caused by catastrophic events
at least five mass extinctions in last 600 million years

42. Speciation often occurs in patterns.
A pattern of punctuated equilibrium exists in the fossil record.
theory proposed by Eldredge and Gould in 1972
episodes of speciation occur suddenly in geologic time
followed by long periods of little evolutionary change
revised Darwin’s idea that species arose through gradual transformations

43. Many species evolve from one species during adaptive radiation.
ancestral species diversifies into many descendent species
descendent species usually adapted to wide range of environments