1. Unit: V.

2. How common is genetic variation All organisms have at least two forms of alleles for each trait some of which are easily observable and other that are “invisible” Population: A group of individuals of the same species that interbreed. Gene Pool: All of the genes that are present in a population. Relative frequency: The number of times an allele occurs in a gene pool compared to the other alleles for the same gene. Evolution: In genetic terms is any change in the relative frequency of alleles in a population.

3. Sources of Genetic Variations: Mutations: Any change in genetic material Gene Shuffling: The mixing or reordering of alleles during sexual reproduction. Are responsible for most heritable genetic differences All of the genes on the 23 pairs of human chromosomes can produce 8.4 million different combinations of genes.

4. Single Gene vs. Polygenic Traits: Single Gene Traits: A trait that is controlled by a single gene that has two alleles. Example (TT) (Tt) Tall and (tt) short. Polygenic Traits: A trait that is controlled by two or more genes often times with each gene having two or more alleles. The number of phenotypes produced for a given trait depends on how many genes control the trait.

5. Natural selection on single-gene traits Natural selection on single gene traits can lead to changes in the allele frequencies and thus to evolution. If a mutation takes place and that mutation gives the organisms an advantage or disadvantage to survival that mutation may control if that mutation becomes a common occurrence within that species.

6. Natural selection on polygenic traits The effects of natural selection on polygenic traits is much more complex because of variations in fitness. Natural selection can affect the distributions of phenotypes in of polygenic traits in three ways. Directional Selection: Occurs when individuals at one end of the distribution curve have a fitness than individuals in the middle or other end of the curve. Stabilizing Selection: Occurs when individuals near the center of a distribution curve have a higher fitness than either end. Disruptive Selection: Occurs when individuals at the upper and lower ends of the distribution curve have higher fitness than individuals in the middle.

7. Genetic Drift: The random change in allele frequencies that occur in small organismal populations. In small populations, individuals that carry a particular allele may leave more descendants than other individuals, just by chance. Over time a series of chance occurrences of the type can cause an allele to become more common in a population. Founder Effect: The change in allele frequencies as a result of the migration of a small subgroup of a population.

8. What happens when no change takes place? Scientists try to use this ideal situation to study what really happens. Evolution Versus Genetic Equilibrium Hardy-Weinberg Principle: States that allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change. Does not exist in reality and is only used for study purposes. If alleles do not change evolution would not occur. Genetic Equilibrium: Allele frequencies remain constant. This requires five conditions to be maintain from generation to generation in order to take place. Random Mating, Large Population, No Movement Into or Out of the Population, No Mutations, No Natural Selection.

9. Speciation: The formation of a new species Factors such as natural selection and random chance events change the relative allele frequencies and lead to the formation of new species. If a genetic change increases fitness that change will eventually be found in many more individuals in a given population. Isolating Mechanisms: Factors that separate populations of the same species and thus separate the gene pools of those populations leading to the formation of new species. Reproductive Isolation: The separation of species or populations so that they cannot interbred Behavioral Isolation: Different courtship rituals or other behavior that prevents them from interbreeding. Geographic Isolation: Species separated by physical geographic barrier like a river, mountain, etc. that prevents interbreeding. Temporal Isolation: Species that reproduce at different times of the year and prevents interbreeding.

10. Darwin’s Finches Are prime examples of evolution using the mechanisms of speciation. Method of evolution of Darwin’s Finches Founders Arrive  Separation of Pop.  Changes in Gene Pool  Reproductive Isolation  Ecological Competition  Continued Evolution. Shows evolution and the mechanisms of speciation naturally occurring in nature. Can be used as a model to predict future patterns of evolution and speciation.