1. Chapter 16 Table of Contents Section 1 Genetic Equilibrium
Population Genetics and Speciation
Chapter 16
Table of Contents
Section 1 Genetic Equilibrium
Section 2 Disruption of Genetic Equilibrium
Section 3 Formation of Species

2. Variation of Traits
Population genetics - The study of evolution from a genetic point of view.
Also known as microevolution - a change in the collective genetic material of a population.
Remember a population is the smallest unit in which evolution can occur.

3. Variation of Traits Within a Population
Section 1 Genetic Equilibrium
Chapter 16
Variation of Traits Within a Population
Population biologists study many different traits in populations, such as size and color.

4. Variation of Traits Within a Population, cont.
Section 1 Genetic Equilibrium
Chapter 16
Variation of Traits Within a Population, cont.
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 (random change in a gene that is passes on), recombination (reshuffling of genes during meiosis due to crossing-over), and the random pairing of gametes (due to the large amounts if gametes).

5. Section 1 Genetic Equilibrium
Chapter 16
The Gene Pool
The total genetic information available in a population is called the gene pool. The number of alleles and frequency of those alleles in a gene.
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.
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.

6. Generation 1 What about generation 2? Phenotypic ratios
4 red (out of 8) frequency = .5,
4 pink (out of 8) frequency =.5,
no white frequency = 0.
Genotypic ratios
12 R (out of 16) frequency = .75
4 r (out of 16) frequency = .25
What about generation 2?

7. The Hardy-Weinberg Genetic Equilibrium
Section 1 Genetic Equilibrium
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.
q+p=1
q2+2pq+p2=1
5 Assumptions for Equilibrium

8. Chapter 16 Causes of Evolution
Section 2 Disruption of Genetic Equilibrium
Chapter 16
Causes of Evolution
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.
Some are harmful and difficult to eliminate, some are helpful, and increase survival.

9. Section 2 Disruption of Genetic Equilibrium
Chapter 16
Gene Flow
Emigration and immigration cause gene flow between populations and can thus affect gene frequencies.
Immigration - Individuals moving into population.
Emigration - Individuals moving out of a population
Gene Flow - the process of genes moving from one population to another through migration or dispersal of seeds and spores.

10. Section 2 Disruption of Genetic Equilibrium
Chapter 16
Genetic Drift
Genetic drift is a change in allele frequencies due to random events.
Genetic drift operates most strongly in small populations, but genetic equilibrium happens in large populations because a change is less effective
Small population, one organism doesn’t mate it could be catastrophic. In large populations, one organism doesn’t mate, the population will still go on.

11. Chapter 16 Nonrandom Mating
Section 2 Disruption of Genetic Equilibrium
Chapter 16
Nonrandom Mating
Mating is nonrandom whenever individuals may choose partners.
Assortative mating - picking a mate that has similar genes to oneself.
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.
Ex. Peacock mating

12. Chapter 16 Natural Selection
Section 2 Disruption of Genetic Equilibrium
Chapter 16
Natural Selection
Natural selection can influence evolution in one of three general patterns.
Stabilizing selection favors the formation of average traits.
Disruptive selection favors extreme traits rather than average traits.
Directional selection favors the formation of more-extreme traits.

13. Three Kinds of Selection
Section 2 Disruption of Genetic Equilibrium
Chapter 16
Three Kinds of Selection

14. Chapter 16 The Concept of Species
Section 3 Formation of Species
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.
Ex. Dogs cannot breed with cats
Speciation – The development of new species
Morphology – the internal and external structure and appearance of an organism, used to classify it as a species.

15. Modern Definition of Species/Speciation
Species – A single kind of organism. Members are morphologically similar and can interbreed to produce fully fertile offspring.
The many species alive today diverged from a smaller group of species.

16. Isolation and Speciation
Section 3 Formation of Species
Chapter 16
Isolation and Speciation
Geographic Isolation
Geographic isolation the physical separation of members of a population by geographic barriers.
Ex. Canyons or Mountains forming.
Allopatric Speciation - the arrival of new species due to geographic isolation.
Happens more often in small populations with a small gene pool because they are more greatly affected by the environment.

17. Chapter 16 Geographic Isolation Section 3 Formation of Species
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Visual Concept

18. Isolation and Speciation, continued
Section 3 Formation of Species
Chapter 16
Isolation and Speciation, continued
Reproductive Isolation results from the separation of population subgroups by barriers to successful breeding.
Disruptive Selection causes this to happen, 2 types of isolation from this.
Prezygotic – before fertilization. (different mating times and calls of frogs.)
Postzygotic – after fertilization. (horse and donkey.)
Sympatric Speciation - Reproductive isolation within the same geographic area.
Ex. If all of a species lives on one type of plant and then some individuals start to live on another plant, they may not longer be able to interbreed with their original population.

19. Reproductive Isolation
Section 3 Formation of Species
Chapter 16
Reproductive Isolation
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Visual Concept

20. Chapter 16 Rates of Speciation Slow over Millions of years
Section 3 Formation of Species
Chapter 16
Rates of Speciation
Slow over Millions of years
In the gradual model of speciation (gradualism), species undergo small changes at a constant rate.
Quick Bursts of Change
Under punctuated equilibrium, new species arise abruptly, differ greatly from their ancestors, and then change little over long periods.

21. Chapter 16 Comparing Punctuated Equilibrium and Gradualism
Section 3 Formation of Species
Chapter 16
Comparing Punctuated Equilibrium and Gradualism
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Visual Concept