AP Biology, Chapter 23
The Evolution of Populations

Summary
Introduction
	1. Explain why it is incorrect to say that individual organisms evolve.
		a. Evolution is the defined as a directional change in gene frequency
		b. An organism contributes over the course of its lifetime

POPULATION GENETICS
	Introduction
	The modern evolutionary synthesis integrated Darwinian selection and Mendelian 
	inheritance
		2. Explain what is meant by "the modern synthesis."
			a. Combines Mendelian genetics, biogeography and population genetics
			b. Explains natural selection in terms of restricted gene flow and selection within 
			populations
	The genetic structure of a population is defined by its allele and genotype frequencies
		3. Define a population; define a species.
			a. Population = local breeding group
			b. Species = group of populations whose individuals have the potential to 
			interbreed and produce fertile offspring
		4. Explain how microevolutionary change can affect a gene pool.
			a. Gene pool = all alleles at all loci in the population
			b. Increase or decrease in allele frequency = microevolution
	The Hardy-Weinberg theorem describes a nonevolving population
		5. State the Hardy-Weinberg theorem.
			a. Allele and genotypic frequencies remain constant unless acted upon
		6. Write the general Hardy-Weinberg equation and use it to calculate allele and genotype 
		frequencies.
			a. Equations for one locus with two alleles with frequencies p and q
				i. p + q = 1
				ii. p2 + 2pq + q2 = 1
			b. Hints for solving problems
				i. If given p or q, subtract from 1 and plug and chug
				ii. If given the frequency of the homozygous recessives, take the square 
				root, subtract from 1, and plug and chug
		7. Explain why the Hardy-Weinberg theorem is important conceptually and historically.
			a. Mathematically defines the population
			b. Starting point for modeling factors affecting change
		8. List the conditions a population must meet to maintain Hardy-Weinberg equilibrium.
			a. Large population
			b. No gene flow
			c. No net mutation
			d. Random mating
			e. No natural selection

CAUSES OF MICROEVOLUTION
	Microevolution is a generation-to-generation change in a population's allele or 
	genotypic frequencies
		9. Define microevolution.
			a. Generation-to-generation change in a population's genetic structure
		10. Define evolution at the population level.
			a. Change in allele and genotypic frequencies in a population
	The five causes of microevolution are genetic drift, gene flow, mutation, nonrandom 
	mating, and natural selection
		11. Explain how genetic drift, gene flow, mutation, nonrandom mating, and natural 
		selection can cause microevolution.
			a. Drift is the random change in gene frequencies; less with more samples
			b. Gene flow allows certain individuals to enter and leave with their genes
			c. Mutation tends to degrade the gene pool
			d. Nonrandom mating denies some their reproductive rights
			e. Natural selection increases or decreases the contributions of some individuals
		12. Explain the role of population size in genetic drift.
			a. "The smaller the sample, the greater the chance of deviations from the 
			expected result."
			b. Small populations are more affected by sampling
		13. Distinguish between the bottleneck effect and the founder effect.
			a. Bottleneck
				i. Down to a small population by random killing
				ii. Randomly eliminates, reduces, or enhances frequencies
				iii. Small population suffers drift
			b. Founder effect: a small population selected by colonization
		14. Explain why mutation has little quantitative effect on a large population.
			a. Mutation rates are about 105 - 106 per locus per generation
			b. Individual loci accumulate mutations slowly

GENETIC VARIATION, THE SUBSTRATE FOR NATURAL SELECTION
	Introduction
	Genetic Variation occurs within and between populations
		15. Explain how quantitative and discrete characters contribute to variation within a 
		population.
			a. Quantitative vary on a continuum from polygenic inheritance
			b. Discrete characters produce distinct phenotypes
		16. Define polymorphism and morphs. Describe an example of polymorphism within the 
		human population.
			a. Definitions
				i. Polymorphism: two or more distinct forms in significant proportion 
				ii. Morphs: the distinct forms
			b. Example: ABO blood groups
		17. Distinguish between gene diversity and nucleotide diversity. Describe examples of 
		each in humans.
			a. Gene diversity = average percentage of loci that are heterozygous
			b. Nucleotide diversity = average percentage of bases that are heterozygous
			c. Human gene diversity = 14%, nucleotide diversity = 0.1%
		18. List some factors that can produce geographic variation among closely related 
		populations. Define a cline.
			a. Factors include: interacting species, drift, microenvironments
			b. Cline: variation graded along a geographic axis
	Mutation and sexual recombination generate genetic variation
		19. Explain why even though mutation can be a source of genetic variability, it 
		contributes a negligible amount to genetic variation in a population.
			a. Most mutations have little or harmful effect
		20. Describe the cause of nearly all genetic variation in a population.
			a. Mutation and rapid selection provide significant variation in microorganisms
			b. Most variation in sexual populations is due to genetic recombination
	Diploidy and balanced polymorphism preserve variation
		21. Explain how genetic variation may be preserved in a natural population.
			a. Recessive alleles remain hidden in diploids
			b. Balanced polymorphism
				i. Heterozygote advantage like in sickle cell
				ii. Hybrid vigor 
				iii. Patchy environment favoring many morphs
				iv. Frequency-dependent selection
		22. Briefly describe the neutral theory of molecular evolution and explain how changes in 
		gene frequency may be nonadaptive.
			a. Some molecular variation has little or no effect on survival and reproductive 
			success
			b. Such variation may drift into significance 
			c. Neutral variation is in reserve for changing circumstances

NATURAL SELECTION AS A MECHANISM OF ADAPTIVE EVOLUTION
	Introduction
	Evolutionary fitness is the relative contribution an individual makes to the gene pool 
	of the next generation
		23. Describe what selection acts on and what factors contribute to the overall fitness of a 
		genotype.
			a. Selection acts on entire phenotype, very rarely on one trait
			b. Fitness is affected by survival, fertility, longevity, environment
		24. Distinguish between Darwinian fitness and relative fitness.
			a. Darwinian fitness: total contribution to the gene pool of the next generation
			b. Relative fitness: contribution of a genotype compared to the competing alleles
		25. Describe examples of how an organism's phenotype may be influenced by the 
		environment.
			a. Malnutrition reduces fertility
			b. The sun darkens
			c. Catastrophes eliminate competition
	The effect of selection on a varying characteristic can be stabilizing, directional, or 
	diversifying
		26. Distinguish among stabilizing selection, directional selection, and diversifying 
		selection.
			a. Stabilizing: selects against the extremes, makes the population more average
			b. Directional: one extreme is selected against, average shifts
			c. Diversifying: both extremes have an advantage, distribution splits
	Sexual selection may lead to pronounced secondary differences between the sexes
		27. Describe the advantages and disadvantages of sexual reproduction.
			a. Advantages
				i. Generates genetic diversity
				ii. Eliminates harmful recessives
				iii. Allows heterozygote advantage
				iv. Enables chromosomal repair
				v. Duplicates for backup
			b. Disadvantages
				i. Requires complex behavioral and physiological adaptations
				ii. Disrupts advantageous combinations in constant environments
				iii. Slower
		28. Define sexual dimorphism and explain how it can influence evolutionary change.
			a. Sexual dimorphism: different forms of the male and female of a species
			b. Influence
				i. Sexes can assume complementary behavioral roles
				ii. Sexes can more efficiently use resources
				iii. May promote selection of "improvements"
		29. Distinguish between intrasexual selection and intersexual selection.
			a. Intrasexual: within a sex; males fighting to determine mating
			b. Intersexual: between sexes; females examine males and select a mate
	Natural selection cannot fashion perfect organisms
		30. Describe at least four reasons why natural selection cannot breed perfect organisms.
			a. Historical constraints: genetic baggage takes a while to wash away
			b. Adaptations are often compromises
			c. Chance
			d. Selection begins with alleles on hand