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BIOLOGY: Chapter 16 “The Evolution of

Populations & Speciation”

Warm-Up: (pg 292)Compare & contrast convergent and

divergent evolution (include examples).

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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.

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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

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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

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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

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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.

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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

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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.

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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.

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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.

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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.

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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

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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.