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BIOLOGY: Chapter 16 “The Evolution of Populations & Speciation”

BIOLOGY: Chapter 16 “The Evolution of Populations & Speciation”. Warm-Up : (pg 292) Compare & contrast convergent and divergent evolution (include examples). Section 16-1: “Genetic Equilibrium”. Section 16-1 Objectives:

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BIOLOGY: Chapter 16 “The Evolution of Populations & Speciation”

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  1. BIOLOGY: Chapter 16 “The Evolution of Populations & Speciation” Warm-Up: (pg 292) Compare & contrast convergent and divergent evolution (include examples).

  2. Section 16-1: “Genetic Equilibrium” • Section 16-1 Objectives: • (1) The student will be able to explain the importance of the bell curve to population genetics. • (2) The student will be able to describe 2 causes of genotypic variation in a population. • (3) The student will be able to explain how to compute allele frequency and phenotype frequency. • (4) The student will be able to explain Hardy-Weinberg genetic equilibrium.

  3. Section 16-1 “Genetic Equilibrium” • Variation of Traits in a Population • Population genetics- the study of evolution from a genetics perspective • Population- collection of individuals of the same species that interbreed; it’s the smallest unit in which evolution can occur • Bell Curve (Fig 16-1, pg 299)- many traits in a population show variation that follows this curve (i.e., height and weight). • Causes of Variation • A. Environmental factors (i.e., food) • B. Heredity • C. Variations in genotypes: • 1. Mutation • 2. Recombination during meiosis • 3. Random fusion of gametes

  4. Section 16-1 “Genetic Equilibrium” • Allele Frequencies & The Gene Pool • Gene pool – the total genetic info available in a population • Allele frequency (pg 300) – divide the # of a certain allele by the total # of alleles of all types in a population. • Predicting Phenotype (Fig 16-3, pg 301) • Phenotype frequency equals # of individual’s w/a particular phenotype divided by total # of individual’s in a population

  5. Section 16-1 “Genetic Equilibrium” • Hardy-Weinberg Genetic Equilibrium • Wilhelm Weinberg, a German physician, & Godfrey Hardy, a British mathematician, independently showed allele frequencies in a population remain the same through each generation unless influenced by outside sources. • It’s based on a set of “assumptions” about an ideal hypothetical population that is NOT evolving (“real” populations may violate conditions needed for genetic equilibrium where allele frequencies don’t change each generation): • 1. NO mutations • 2. Individuals don’t leave a population • 3. Large population • 4. Random mating • 5. NO selection • http://en.wikipedia.org/wiki/Hardy-Weinberg_principle

  6. Section 16-2: “Disruption of Genetic Equilibrium” • Section 16-2 Objectives: • (1) The student will be able to list 5 conditions that can cause evolution to occur. • (2) The student will be able to give an example of how migration can effect evolution. • (3) The student will be able to define genetic drift, and tell how it affects endangered species. • (4) The student will be able to contrast the effects of stabilizing, directional, and disruptive selection on variations in a trait over time. • (5) The student will be able to give an example of sexual selection.

  7. Section 16-2 “Disruption of Genetic Equilibrium” • Requirements of genetic equilibrium: • 1. Mutation • Genetic equilibrium requires that allele frequencies do not change because of mutations. • Genetic mutations disrupt genetic equilibrium by producing new alleles for a trait. • 2. Migration • Genetic equilibrium requires that a population stays constant. • Ways to change gene frequencies: • Immigration – movement “into” a population • Emigration - movement “out” of a population • Gene flow - genes move from one population to another

  8. Section 16-2 “Disruption of Genetic Equilibrium” • 3. Genetic Drift • Genetic equilibrium requires the presence of a large population. • Genetic drift is only significant in small and medium-sized populations. • Genetic drift – allele frequencies in a population change as a result of random events, or chance (Figure 16-6, pg 305). • 4. Nonrandom Mating • Genetic equilibrium requires random mating, regardless of genetic makeup. • Assortative mating - selection of a mate based on similar characteristics. • Nonrandom mating can affect genotypes, but it does not affect overall allele frequencies.

  9. Section 16-2 “Disruption of Genetic Equilibrium” • 5. Natural Selection- Genetic equilibrium requires the absence of natural selection. • Figure 16-7, pg 307!!! • Stabilizing Selection - individuals with the average form of a trait have the highest fitness. • Directional Selection – individuals that display a more extreme form of a trait have a greater fitness than individuals with an average form of the trait. • Disruptive Selection - individuals with either an extreme variation of a trait have a greater fitness than individuals with an average form of the trait. • Sexual Selection – Females tend to choose the males as mates based on certain traits.

  10. Section 16-3 “Formation of Species” • Section 16-3 Objectives: • (1) The student will be able to explain the difference between the morphological concept of species and the biological species concept. • (2) The student will be able to define geographic isolation, and explain how it can lead to speciation. • (3) The student will be able to name 2 kinds of reproductive isolation. • (4) The student will be able to summarize the punctuated equilibrium hypothesis, and contrast it with the hypothesis of gradual change.

  11. Section 16-3 “Formation of Species” • The Concept of Species • Speciation – process of species formation; existing species are changed versions of older species; results in many related populations • Morphological Concept of Species • Morphology – the internal & external structure and appearance of an organism; basis for species classification • This concept is limited because there can be phenotypic differences among individuals in a single population (Figure 16-9, pg 309). • The Biological Species Concept • Ernst Mayr, German born/American biologists, defined a species as a population of organisms that can successfully interbreed but cannot breed with other groups. • Definition does not match extinct organisms or ones who reproduce asexually since the reproductive abilities cannot be tested.

  12. Section 16-3 “Formation of Species” • Isolating Mechanisms • Geographic Isolation – physical separation of individuals in a population, such as when a habitat becomes divided. • Natural selection & genetic drift causes 2 subpopulations to diverge (differ), eventually causing mating to not occur • Reproductive Isolation – results from barriers to successful breeding between population groups in the same area. • Results in genetic variations • 2 types of reproductive isolation: • 1. Prezygotic isolation – occurs “before” fertilization • 2. Postzygotic isolation – occurs “after” fertilization

  13. Section 16-3 “Formation of Species” • Rates of Speciation • Fossil record shows that many species existed without change for long periods of time. • Punctuated equilibrium – the hypothesis that evolution proceeds at an irregular rate, with short periods of rapid evolution followed by long periods where no evolution occurs.

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