4: Evolutionary Processes
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Transcript of 4: Evolutionary Processes
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Evolutionary Processes
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Human Chromosomes
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Evolution
• Evolution is change in gene (allele) frequencies in populations over time.
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Species
Species: a group of organisms that, under normal circumstances, can breed with each other and have viable, fertile offspring.
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Dogs and Wolves = Same Species
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Horse x Donkey =
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Mule
• Mules are a hybrid species. While they have positive features of both parents they are almost always sterile: i.e. they cannot reproduce;
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(male) Lion x (female) Tiger
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Ligers
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(male) Tiger x (female) Lion
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Tigon
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Species, Population and Evolution
Important to remember: evolution occurs within populations, NOT individuals.
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Breeding Population
• Breeding populations are populations within a species that are genetically isolated from each other, typically by geography.
• Gene pool = all the genes carried by all the members of such a group.
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Gene Frequency
• Gene frequency : how frequently a particular gene is found within a given population.
• For instance, you could say that 20% (or 30% or 90%) of a population carry a particular gene (allele)
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Means of Evolution
• Mutation
• Natural Selection
• Genetic Drift
• Gene Flow
• Artificial Selection
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Mutation and Evolution
• Mutations are random changes in genetic material that occur within individuals.
• Mutations are what allow for the emergence of new traits within a population.
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Natural Selection
• Natural selection: certain traits provide an advantage in a particular environment. Individuals with such traits are more likely to pass on their genes to offspring.
• Natural selection is sometimes summarized as “the survival of the fittest.”
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Genetic Drift
Genetic drift represents changes in gene frequencies due to random chance.
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Example of Genetic Drift: The Founder’s Effect
Original Population = 50% Blue eyes and 50% Brown eyes
From this group a small population separate. Coincidentally, there is a high frequency of
brown eyes in this group
New Group= 80% Brown Eyes and 20% Blue Eyes
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Gene Flow and Evolution
Gene Flow: when new individuals enter a breeding population and add their genes to the gene pool.
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Artificial Selection
• Artificial Selection represents breeding other organisms in order for them to display particular traits.
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Speciation
• Speciation refers to the emergence of two or more species from a common ancestor.
• Species represent genetically isolated groups because of their inability to breed with each other.
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Language exercise
• Italian: Pietra
• Portuguese: Pedra
• Spanish: Piedra
• Catalan: Pedra
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Language exercise
Latin: Petra
Italian: Pietra Portuguese Pedra
Spanish: Piedra Catalan: Pedra
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Common Ancestor
• Common ancestor: the ancestor of two or more different species.
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Shared derived characteristic
• Shared derived characteristic: features shared by two or more taxonomic groups that are derived from a common ancestor.
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Horse
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Onager
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Zebra
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Donkey
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Hyracotherium fossil
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Evolution of Equines
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“Zonkey” (Zebra-Donkey Hybrid)
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Homologous Structures
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Analogous Structures