1. Speciation Genetic Equilibrium Disruption of Genetic Equilibrium
Formation of Species

2. Genetic Equilibrium

3. Species: a group of individuals that look similar and whose members are capable of producing fertile offspring in the natural environment

4. Morphological Species Concept
Morphological Species Concept: the idea that organisms can be classified by differences in their appearance
Using this concept, scientists can readily communicate about the characteristics, behavior, and relationships of organisms.
The morphological concept of species is limited because it does not account for the reproductive compatibility of morphologically different organisms.

6. Biological Species Concept
Biological Species Concept: the idea that organisms can be classified by their ability to breed with one another
Using both the biological and morphological concepts of species, modern scientists have arrived at the current definition of the term species.

7. Species: a group of individuals that look similar and whose members are capable of producing fertile offspring in the natural environment

8. Variation of Traits in a Population
Population: all the members of a species that live in the same area and make up a breeding group
Within a population, individuals vary in many observable traits.

9. Caribou
Population
Distribution

10. Variation is the Raw Material of Natural Selection

11. Variation of Traits in a Population

12. What causes variation in traits?
Environmental Factors
Heredity
A difference in genotype usually results in a difference in phenotype.
Variations in genotypes arise through:
Mutation
Genetic Recombination
Independent Assortment
Crossing Over

13. Allele Frequencies and Genetic Equilibrium
Gene Pool: all the genes for all the traits in a population
Allele Frequency: the percentage of an allele in a gene pool
Genetic Equilibrium: the condition in which allele frequencies in a population do not change from generation to generation

14. Genotypic and Allele Frequencies

15. Hardy & Weinberg
Hardy and Weinberg outlined the conditions necessary for genetic equilibrium.
Godfrey Hardy
Wilhelm Weinberg

16. Hardy-Weinberg Principle
Hardy and Weinberg outlined the conditions necessary for genetic equilibrium.
1. no mutations occur
2. individuals neither enter nor leave the population through migration
3. the population is large
4. individuals mate randomly
5. natural selection does not occur

17. Hardy-Weinberg Principle
If one of these conditions does not hold true, allele frequencies of the population may change. In other words, evolution will occur.

18. Disruption of Genetic Equilibrium

19. Disruption of Genetic Equilibrium
Evolution occurs when genetic equilibrium is disrupted.

20. 1. Mutation
Mutations affect genetic equilibrium by producing totally new alleles for a trait.
In addition, mutations can change the frequency of the alleles already present in the gene pool.
The occurrence of mutation in most alleles is too low to cause major changes in the allele frequencies of an entire population.

21. 1. Mutation

22. 2. Migration
Migration: the movement of individual organisms into or out of a population, community, or biome
Immigration: movement of new individuals into a population
Emigration: departure of individuals from a population
Gene Flow: the movement of genes into or out of a population

23. 2. Migration

24. 3. Genetic Drift
Genetic Drift: a shift in allele frequencies in a population due to random events or chance
In small populations, chance can significantly affect allele frequencies from one generation to the next.

25. 3. Genetic Drift

26. 3. Genetic Drift

27. 4. Non-Random Mating
If animals chose their mates then certain traits would be selected for over less desirable ones.

28. 5. Natural Selection
Natural selection is an ongoing process in nature, and is the single most significant factor disrupting genetic equilibrium.

29. 4 Types of Natural Selection
Stabilizing Selection
Directional Selection
Disruptive Selection
Sexual Selection

30. Stabilizing Selection
Stabilizing Selection: a type of natural selection in which the average form of a trait causes an organism to have an advantage in survival and reproduction
The extreme forms of the trait confer a disadvantage to the organism.
Stabilizing selection is most effective in a population that has become well adapted to its environment.
Stabilizing selection is the most common type of NS.

32. Directional Selection
Directional Selection: a type of natural selection in which the distribution of a trait is shifted toward one of the extremes

34. Disruptive Selection
Disruptive Selection: natural selection in which individuals with either of the extreme forms of a trait have an advantage in terms of survival and reproduction
The average form of the trait confers a selective disadvantage to the organism.

36. Sexual Selection
Sexual Selection: the preferential choice of a mate based on the presence of a specific trait
Sexual selection may be stabilizing, directional, or disruptive.

38. Formation of Species

39. Speciation
Disruption of genetic equilibrium leads to changes in the gene pool of a population.
Natural selection causes the most significant genetic changes in a population, however, such changes do not necessarily lead to speciation.
Speciation: the formation of a new species

40. Speciation

41. Speciation

42. Isolated Populations
For a new species to arise, either interbreeding of the population of fertile offspring must somehow cease among members of a formerly successful breeding population.
For this to occur, populations or segments of populations must somehow become isolated.
Two Forms of Isolation:
Geographic Isolation
Reproductive Isolation

43. Geographic Isolation
Geographic Isolation: the physical separation of populations
Examples: population becomes divided by land or water barrier, colonization of new island, river changes course, highway built across field, etc.

44. Reproductive Isolation
Reproductive Isolation: the inability of formerly interbreeding organisms to produce offspring
Reproductive isolation can occur through disruptive selection.

45. Rates of Speciation
Punctuated Equilibrium: a theory that speciation may occur during brief periods of rapid genetic change
Gradualism: a theory that speciation may occur through a gradual change of adaptations
Extinct: the state of a species that no longer exists
For a species to continue to exist, some members must have traits that allow them to survive and pass their genes on to the next generation.