population genetics and speciation chapter 16 table of contents section 1 genetic equilibrium...

Population Genetics and SpeciationChapter 16

Table of Contents

Section 1 Genetic Equilibrium

Section 2 Disruption of Genetic Equilibrium

Section 3 Formation of Species

Chapter 16

Objectives

• Identify traits that vary in populations and that may be studied.

• Explain the importance of the bell curve to population genetics.

• Compare three causes of genetic variation in a population.

• Calculate allele frequency and phenotype frequency.

• Explain Hardy-Weinberg genetic equilibrium.


Chapter 16

Variation of Traits Within a Population

• Population biologists study many different traits in populations, such as size and color.


Chapter 16

Variation of Traits Within a Population, continued• Causes of Variation

– Traits vary and can be mapped along a bell curve, which shows that most individuals have average traits, whereas a few individuals have extreme traits.

– Variations in genotype arise by mutation, recombination, and the random pairing of gametes.


Chapter 16

The Gene Pool

• The total genetic information available in a population is called the gene pool.


Chapter 16

The Gene Pool, continued

• Allele frequency is determined by dividing the total number of a certain allele by the total number of alleles of all types in the population.


Chapter 16

The Gene Pool, continued

• Predicting Phenotype– Phenotype frequency is equal to the number of

individuals with a particular phenotype divided by the total number of individuals in the population.


Chapter 16

The Hardy-Weinberg Genetic Equilibrium

• Allele frequencies in the gene pool do not change unless acted upon by certain forces.

• Hardy-Weinberg genetic equilibrium is a theoretical model of a population in which no evolution occurs and the gene pool of the population is stable.


Chapter 16

Phenotype Frequency


Chapter 16

Objectives

• List five conditions under which evolution may take place.

• Explain how migration can affect the genetics of populations.

• Explain how genetic drift can affect populations of different sizes.

• Contrast the effects of stabilizing selection, directional selection, and disruptive selection on populations over time.

• Identify examples of nonrandom mating.


Chapter 16

Mutation

• Evolution may take place when populations are subject to genetic mutations, gene flow, genetic drift, nonrandom mating, or natural selection.

• Mutations are changes in the DNA.


Chapter 16

Gene Flow

• Emigration and immigration cause gene flow between populations and can thus affect gene frequencies.


Chapter 16

Genetic Drift

• Genetic drift is a change in allele frequencies due to random events.

• Genetic drift operates most strongly in small populations.


Chapter 16

Nonrandom Mating

• Mating is nonrandom whenever individuals may choose partners.


Chapter 16

Nonrandom Mating, continued

• Sexual Selection – Sexual selection occurs when certain traits

increase an individual’s success at mating. – Sexual selection explains the development of traits

that improve reproductive success but that may harm the individual.


Chapter 16

Natural Selection

• Natural selection can influence evolution in one of three general patterns.


Chapter 16

Natural Selection, continued

• Stabilizing Selection – Stabilizing selection favors the formation of

average traits.


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• Disruptive Selection – Disruptive selection favors extreme traits rather

than average traits.


Chapter 16


• Directional Selection – Directional selection favors the formation of

more-extreme traits.


Chapter 16Section 2 Disruption of Genetic Equilibrium

Two Kinds of Selection

Chapter 16

Objectives

• Relate the biological species concept to the modern definition of species.

• Explain how the isolation of populations can lead to speciation.

• Compare two kinds of isolation and the pattern of speciation associated with each.

• Contrast the model of punctuated equilibrium with the model of gradual change.


Chapter 16

The Concept of Species

• According to the biological species concept, a species is a population of organisms that can successfully interbreed but cannot breed with other groups.


Chapter 16

Isolation and Speciation

• Geographic Isolation– Geographic isolation results from the separation

of population subgroups by geographic barriers.


Chapter 16

Click below to watch the Visual Concept.

Visual Concept

Geographic Isolation


Chapter 16

Isolation and Speciation, continued

• Allopatric Speciation– Geographic isolation may lead to allopatric

speciation.


Chapter 16


• Reproductive Isolation– Reproductive isolation results from the

separation of population subgroups by barriers to successful breeding.


Chapter 16


Visual Concept

Reproductive Isolation


Chapter 16


• Sympatric Speciation– Reproductive isolation within the same geographic

area is known as sympatric speciation.


Chapter 16

Rates of Speciation

• In the gradual model of speciation (gradualism), species undergo small changes at a constant rate.

• Under punctuated equilibrium, new species arise abruptly, differ greatly from their ancestors, and then change little over long periods.


Chapter 16


Visual Concept

Comparing Punctuated Equilibrium and Gradualism


population genetics and speciation chapter 16 table of contents section 1 genetic equilibrium...

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