Evolution Speciation I Evolution as Genetic Change A

Evolution: Speciation

I. Evolution as Genetic Change A. Natural Selection on single-gene traits can lead to changes in allele frequencies and thus to evolution B. Natural Selection on polygenic traits can affect the distributions of phenotypes in 3 ways: 1. Directional Selection: towards 1 extreme 2. Stabilizing Selection: towards the middle 3. Disruptive Selection: towards both extremes C. Genetic Drift: unlike natural selection, is a change in gene frequency due to random chance

I. Evolution as a Genetic Change

I. Evolution as Genetic Change D. Evolution vs. Genetic Equilibrium: 5 conditions are required to maintain genetic equilibrium: 1. Random Mating 2. Large Population 3. No Migration 4. No Mutations 5. No Natural Selection E. Hardy-Weinberg principle says allele frequency will remain constant unless 1 or more factors causes change

Reproductive Isolation results from Isolating mechanisms which include Behavioral isolation Geographic isolation Temporal isolation produced by Behavioral differences Physical separation Different mating times which result in Independently evolving populations which result in Formation of new species

II. The Process of Speciation A. Isolating Mechanisms 1. Behavioral Isolation: mating behaviors of two populations differ. (Courtship displays, nest-building, male competition)

II. The Process of Speciation 2. Geographic Isolation: physical distance separates two populations

II. The Process of Speciation 3. Temporal Isolation-two populations reproduce at different times (different mating seasons) 4. Reproductive Isolation-two populations are genetically isolated because they cannot produce fertile offspring. Examples: dog x cat= gametes are incompatible

II. The Process of Speciation B. Species vs. Population 1. Evolution acts on the phenotype of a population. 2. Once a population has evolved enough that it can no longer interbreed with surrounding populations, it can be labeled as a new species. 3. A species is a group of organisms that normally interbreed in nature to produce fertile offspring. a. Horse X Donkey = Mule (non-fertile) b. Bottlenose and Atlantic spotted dolphins (produces a fertile hybrid) c. Lion X Tiger = Liger (does not occur due to geographical isolation. )

Mule Liger

III. DNA and Bootstrapping A. DNA Bootstrapping is a process of using computer analyses of DNA sequences from different species to compare DNA similarities and develop cladograms to indicate relatedness and descent.