Evidence & Processes of Evolution

Processes of Evolution – Summary

Allele Frequency Allele Frequency – the number of alleles for a specific trait that occur in a population Ex. The number of A’s vs a’s Natural selection shifts the phenotypic distribution away from the phenotype that is selected against

Mechanisms of Evolution Natural Selection “survival of the fittest” Mutations create new alleles Migration moves alleles into and out of a population Genetic drift happens when random events change the allele frequencies of small populations Sexual Selection (non-random mating)

Natural Selection http://www.youtube.com/watch?v=aTftyFboC_M

Species A group of organisms that can interbreed in nature and produce fertile offspring

Speciation – How New Species Form Must be isolated from other populations for a long period of time. different selection pressures cause different traits to be selected for or against.

http://www.youtube.com/watch?v=2oKlKmrbLoU

Geographic Isolation Species are separated from each other by a physical barrier

Geographic Isolation The Kaibab and Albert squirrels are separated by the Grand Canyon

Behavioral Isolation Species cannot interbreed because they have different mating rituals or behavior

Temporal Isolation Species mate at different times of the day or the year

Mass Extinctions When many species disappeared from the Earth Provides opportunity for new species to evolve and establish themselves Mammals might not have “taken over” if the dinosaurs hadn’t gone extinct!

Adaptive Radiation A single species evolves into many species Occurs as new opportunities for survival arise

Convergent Evolution Unrelated organisms begin to look like each other because of similar selection pressures These organisms would have analogous structures

Convergent Evolution Sharks (fish) and dolphins (mammals) have evolved similar adaptations because of similar selective pressures

Coevolution When two species evolve together in response to changes in each other Example: Bees and Flowers

Evidences of Evolution

Homologous Structures Similar body structures that are adapted in different ways for different organisms Provide evidence that related organisms descended, with modifications, from a common ancestor

Vestigial Structures The structures of organisms that remain from a common ancestor, but may no longer affect its ability to survive and reproduce Example: Appendix, Tail Bone

Analogous Structures Unrelated organisms in similar environments develop similar adaptations. Example: Flight of Insects vs. Birds vs. Bats

Fossil Record The fossilized remains of organisms found in the layers of rock and soil Shows that the diversity of organisms has changed over time

Embryology Organisms with a common ancestor share similar stages of development.

DNA Analysis All organisms use the same four bases for their DNA (genetic code). The more similar two sequences of DNA are, the more recent their common ancestor, or the more closely related the organisms are.

DNA Analysis Modern biologists compare DNA sequences to determine which organisms are most-closely related to each other