1. Chapter 16 Objectives Section 1 Genetic Equilibrium
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.

2. 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.
Population genetics – study of evolution from a genetic point of view
For example: Studying dogwood trees in Middletown, Connecticut would be a way to describe a population

3. Variation of Traits Within a Population, continued
Section 1 Genetic Equilibrium
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.

4. Section 1 Genetic Equilibrium
Chapter 16
The Gene Pool
The total genetic information available in a population is called the gene pool.

5. The Gene Pool, continued
Section 1 Genetic Equilibrium
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.

6. The Gene Pool, continued
Section 1 Genetic Equilibrium
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.
Allele frequencies in the gene pool do not change unless acted upon by certain forces.

7. Section 1 Genetic Equilibrium
Chapter 16
Phenotype Frequency

8. The Hardy-Weinberg Genetic Equilibrium
Section 1 Genetic Equilibrium
Chapter 16
The Hardy-Weinberg Genetic Equilibrium
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.
Certain conditions are needed: no mutations occur, the population is infinitely large, individuals neither leave nor enter the population

9. Chapter 16 Objectives Section 2 Disruption of Genetic Equilibrium
Explain how migration can affect the genetics of equilibrium
Explain how genetic drift can affect populations of different sizes.

10. Section 2 Disruption of Genetic Equilibrium
Chapter 16
Gene Flow
Immigration – the movement of individuals into a population
Emigration – movement of individuals out of a population
If individuals are moving in or out a population the genetics of that population will change…if individuals move, genes move with them.

11. Section 2 Disruption of Genetic Equilibrium
Chapter 16
Genetic Drift
Genetic Drift is the phenomenon by which allele frequencies in a population change as a result of random events, or chance.
The larger the population the more stable the genetics will stay, the smaller the more things can change.
Figure 16-5

12. Chapter 16 Objectives Section 3 Formation of Species
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.

13. Chapter 16 The Concept of Species
Section 3 Formation of Species
Chapter 16
The Concept of Species
Speciation - formation of new species as a result of evolution
Morphology – study of the structure and form of an organism (this is the major way to classify organisms)
Major limitations of the morphological concept:
There may be a great deal of phenotypic variability in a species
Organisms that actually can interbreed may have very different physical characteristics
It does not consider whether individuals of a species can mate and produce viable offspring

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.

15. Isolation and Speciation
Section 3 Formation of Species
Chapter 16
Isolation and Speciation
Geographic Isolation
Geographic isolation results from the separation of population subgroups by geographic barriers
Ex. Canyon could form to divide a population
Speciation can occur as a result of geographic isolation because populations that live in different environments may be exposed to different selection pressures

16. Isolation and Speciation, continued
Section 3 Formation of Species
Chapter 16
Isolation and Speciation, continued
Allopatric Speciation
Geographic isolation may lead to allopatric speciation.
When this occurs new species arise as a result of geographic isolation

17. Isolation and Speciation, continued
Section 3 Formation of Species
Chapter 16
Isolation and Speciation, continued
Reproductive Isolation
Reproductive isolation results from the separation of population subgroups by barriers to successful breeding.
Two types of reproductive isolation
Prezytoic – occurs before fertilization
Postzygotic – occurs after fertilization
Reproductive isolation differs from geographic isolation in that members of the same species are not physically separated in repro. Isolation, whereas they are separated in geo. separation

18. Isolation and Speciation, continued
Section 3 Formation of Species
Chapter 16
Isolation and Speciation, continued
Sympatric Speciation
Sympatric speciation occurs when two subpopulations become reproductively isolated within the same geographic area
Ex. A population of insects might live on a single type of plant. If some of the individuals from this population began to live on another type of plant, they would no longer interbreed with the original population

19. Chapter 16 Rates of Speciation
Section 3 Formation of Species
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.