1. Process of Evolution
Chapter 18
Mader: Biology 8th Ed.

2. Evolution in a Genetic Context - Microevolution Hardy-Weinberg
Outline
Evolution in a Genetic Context
- Microevolution
Hardy-Weinberg
Causes of Microevolution
Natural Selection
Types of Selection
Maintenance of Variations
Speciation
Modes of Speciation
Mader: Biology 8th Ed.

3. Evolution in a Genetic Context
Microevolution
In population genetics, the various alleles at all the gene loci in all individuals make up the gene pool of the population.
To determine the frequency of each allele, calculate its percentage from the total number of alleles in the population.
Mader: Biology 8th Ed.

4. Hardy-Weinberg
The Hardy-Weinberg principle states an equilibrium of allele frequencies in a gene pool, p2 + 2pq + q2, will remain in effect in each succeeding generation of a sexually reproducing population, assuming:
No Mutations
No Gene Flow
Random Mating
No Genetic Drift
No Selection
Mader: Biology 8th Ed.

5. Evolution has occurred.
Hardy-Weinberg
Under real conditions, these conditions are rarely, if ever, met, and allele frequencies in the gene pool of a population change between generations.
Evolution has occurred.
Accumulation of small changes is referred to as microevolution.
Mader: Biology 8th Ed.

6. Industrial Melanism
Mader: Biology 8th Ed.

7. Causes of Microevolution
Genetic Mutations
Once alleles have mutated, certain combinations of alleles might be more adaptive than others in a particular environment.
Gene Flow
Movement of alleles between populations by migration of breeding individuals.
Continual gene flow reduces variability between populations.
Mader: Biology 8th Ed.

8. Gene Flow
Mader: Biology 8th Ed.

9. Causes of Microevolution
Nonrandom Mating
Individuals do not choose mates randomly.
Assortative mating - Individuals tend to mate with those with the same phenotype.
Sexual selection - Males compete for the right to reproduce and females choose to mate with males possessing a particular phenotype.
Mader: Biology 8th Ed.

10. Causes of Microevolution
Genetic Drift
Changes in allele frequencies of a gene pool due to chance.
Larger effect in small populations.
Mader: Biology 8th Ed.

11. Genetic Drift
Mader: Biology 8th Ed.

12. The alleles carried by population founders are dictated by chance.
Genetic Drift
Bottleneck Effect
An event prevents a majority of genotypes from entering the next generation.
Founder Effect
Rare alleles occur at a higher frequency in a population isolated from the general population.
The alleles carried by population founders are dictated by chance.
Mader: Biology 8th Ed.

13. Differential Adaptiveness Differential Reproduction Relative Fitness
Natural Selection
Natural Selection is the process that results in adaptation of a population to the biotic and abiotic environment. Requires:
Variation
Inheritance
Differential Adaptiveness
Differential Reproduction
Relative Fitness
Mader: Biology 8th Ed.

14. Directional Selection
Types of Selection
Directional Selection
An extreme phenotype is favored and the distribution curve shifts in that direction.
Can occur when a population is adapting to a changing environment.
Mader: Biology 8th Ed.

15. Directional Selection
Mader: Biology 8th Ed.

16. Stabilizing Selection
Types of Selection
Stabilizing Selection
Occurs when an intermediate phenotype is favored.
Can improve adaptation of the population to constant conditions.
Mader: Biology 8th Ed.

17. Stabilizing Selection
Mader: Biology 8th Ed.

18. Two distinctly different phenotypes are found in the population.
Types of Selection
Disruptive Selection
Two or more extreme phenotypes are favored over any intermediate phenotype.
Two distinctly different phenotypes are found in the population.
Mader: Biology 8th Ed.

19. Disruptive Selection
Mader: Biology 8th Ed.

20. Maintenance of Variations
Maintenance of variation is beneficial because populations with limited variation may not be able to adapt to new conditions.
Only exposed alleles are subject to natural selection.
Sickle-Cell Disease
Homozygote remains in equilibrium in some regions of Africa because the heterozygote is protected from sickle-cell and malaria.
Mader: Biology 8th Ed.

21. Sickle-Cell Disease
Mader: Biology 8th Ed.

22. Reproductive Isolation Phylogenetic
Speciation
Speciation is the splitting of one species into two or more species, or the transformation of one species into a new species over time.
Species Definition
Morphological
Biological
Reproductive Isolation
Phylogenetic
Mader: Biology 8th Ed.

23. Reproductive Isolating Mechanisms
Prezygotic Isolating Mechanisms
Prevent reproduction attempts, and make it unlikely fertilization will be successful.
Habitat Isolation
Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Gamete Isolation
Mader: Biology 8th Ed.

24. Reproductive Isolating Mechanisms
Postzygotic Isolating Mechanisms
Prevent hybrid offspring from developing or breeding.
Zygote Mortality
Hybrid Sterility
F2 Fitness
Mader: Biology 8th Ed.

25. Allopatric Speciation
Modes of Speciation
Allopatric Speciation
Occurs when one population is geographically isolated from other populations.
Sympatric Speciation
A population develops into two or more reproductively isolated groups without prior geographic isolation.
Mader: Biology 8th Ed.

26. Adaptive Radiation is an example of allopatric speciation.
Many new species evolve from a single ancestral species when members of the species become adapted to different environments.
Mader: Biology 8th Ed.

27. Mader: Biology 8th Ed.

28. Evolution in a Genetic Context - Microevolution Hardy-Weinberg
Review
Evolution in a Genetic Context
- Microevolution
Hardy-Weinberg
Causes of Microevolution
Natural Selection
Types of Selection
Maintenance of Variations
Speciation
Modes of Speciation
Mader: Biology 8th Ed.

29. Mader: Biology 8th Ed.