Process of Evolution

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

2. 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. 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. 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. 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. 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. 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. 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. 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. 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 • 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. 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.