What is evolution? A gradual change in the genes of a population of organisms over time.
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Transcript of What is evolution? A gradual change in the genes of a population of organisms over time.
What is evolution?
A gradual change in the genes of a population of organisms
over time
What is meant by “last common ancestor?”
You Cousin
AuntMom
GrandparentLast common ancestor of you and
your cousin
Evolution is a theory.What does this mean?
• A theory in science is a well tested explanation of observable events supported by experimental evidence collected over time.
Charles Darwin’s Theory of Evolution
• Individuals with the best adaptations for their environment survive and pass on their genes (natural selection)
• All living species compete with each other for survival
• All living things change over time• All species on earth (both alive and
extinct) share a common heritage
Darwin’s Theory of Evolution by Natural Selection
• Charles Darwin devised the theory of evolution by natural selection and published it in 1858
• Natural Selection: organisms best adapted to their environment survive, reproduce, and pass on their traits
• Examples of natural selection
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Charles Darwin (1860 at age 51)
Bacterial Growth - no antibiotic present
Mutation makesbacteria resistant to drugs
Antibiotic is present
Drug-resistant bacteria survive and reproduce
ANTIBIOTIC RESISTANCE
Evidence for Evolution
• Fossil Record • Homologous and vestigial
structures• Comparative embryology • Biochemical (DNA, RNA,
proteins)
Fossil Record
• Shows changes in a species over the course of time
• Older fossils are in bottom rock layers
• Radioisotope dating is used to determine the age of the rock the fossils are in Older fossils are in lower layers;
younger fossils are in higher layers.
Homologous Structures
• Structures with the same design, but serve a different purpose (ex. Human arm, cat leg, flipper of a whale)
• Similarities in the structures suggest that the organisms shared a common ancestor.
Four homologous structures.Note the similarity in the structureof each
Vestigial Structures
A structure that is present in anorganism but no longer serves its
original purpose
examples
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Embryological similarities
• Early embryos of many species look very similar
• The genes for early development of embryos are the same or similar for many species
• Suggests a common ancestor whom had these developmental genes
Embryos of different vertebratespecies
Biochemical Comparisons
• Similarities in the genes and proteins of different species
• Closely related organisms share a high percentage of similarity in their DNA sequences
• Homeotic genes determine what structures develop where in an organism (ex. The placement and structure of the arms and legs)
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Evolution of PopulationsEvolution of Populations
Population GeneticsPopulation Genetics
Populations evolve, NOT individuals
Changes in the Gene Pool
• Evolution is caused by changes in the gene pool of a population
• A gene pool is all of the genes in a population of a species
• The frequency of an allele in the gene pool is known as allelic frequency
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What causes change in the Gene Pool?
• Mutations
• Natural Selection
• Gene flow (movement of genes into or out of the gene pool)
• Genetic drift (changes in allele frequency due to chance events)
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Gene flow between two populations
Speciation - the formation of a new species
• Members of a population become isolated from each other
• Each new population evolves through natural selection with no gene flow between populations
• Over time, the gene pool of each population changes due to natural selection and genetic drift
• When members from the two populations can no longer successfully reproduce with one another, they are said to be different species
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Speciation experiment withfruit flies (click picture for another example)
Isolating mechanisms that cause speciation
• Geographic - a natural barrier prevent two groups from interbreeding
• Temporal - different mating seasons prevent individuals from mating
• Behavioral - different behaviors prevent interbreeding between populations
* All of the above may lead to reproductive isolation (the two groups can no longer mate successfully)
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Geographic isolation by a barrier preventing gene flow between populations