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Evolution. Evolution. Change in genetic frequencies through generations Descent with modification Must be genetic and passed on to offspring . Evidence for evolution Fossil Biochemical (DNA) Anatomical . Mechanisms of Change.
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Evolution • Change in genetic frequencies through generations • Descent with modification • Must be genetic and passed on to offspring • Evidence for evolution • Fossil • Biochemical (DNA) • Anatomical
Mechanisms of Change • All of the following change the frequency in the genes of a population • Mutation • Migration (gene flow) • Genetic drift • Natural selection
Mutation • A mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make the genes for brown beetles more frequent in the population.
Migration • Some individuals from a population of brown beetles might have joined a population of green beetles. That would make the genes for brown beetles more frequent in the green beetle population.
Genetic Drift • Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation—but just by chance. These chance changes from generation to generation are known as genetic drift.
Genetic Drift • Bottleneck • occur when a population’s size is reduced for at least one generation. For example, a hurricane comes through and greatly reduces a population • Reduces genetic variation because the individuals left do not have the same gene frequency as the original population • Founder effect • a new colony is started by a few members of the original population. This small population size means that the colony may have: • reduced genetic variation from the original population. • a non-random sample of the genes in the original population.
Natural Selection • Green beetles are easier for birds to spot (and hence, eat). Brown beetles are more likely to survive to produce offspring. They pass their genes for brown coloration on to their offspring. So in the next generation, brown beetles are more common than in the previous generation.
Types of Natural Selection • The following are types of natural selection: • Stabilizing • Disruptive • Directional
Stabilizing • Selection against two extremes of a trait • Predators can see the bright green frogs and the lightly colored frogs, but the medium colored frogs have better camouflage and are not seen as easily.
Directional selection • Selection against one extreme so the trait drifts towards the other extreme • The bright colored frogs are faster than the others. The medium colored frogs are faster than the light colored frogs.
Disruptive • Individuals with the middle, or medium, trait are selected against. The traits at the extreme increase. • Fast gazelles out run lions, slow gazelles are too skinny for the lions to eat.
Which one? • Moles that are too large sometimes can not fit into their burrows, while moles that are too small often die of starvation.
Which one? • Giraffes with tall necks reach more leaves. The giraffes with short necks can not reach many leaves.
Which one? • A plant that is too short may not be able to compete with other plants for sunlight. However, extremely tall plants may be more susceptible to wind damage
Speciation • What is a species? • How does a species evolve into a new one?
Speciation • Speciation is a lineage-splitting event that produces two or more separate species. • How does this happen?? • Geographic isolation • Reduction of gene flow
Geographic isolation • A species is separated geologically • Different habitats lead to different trait selection • Two separate species eventually
Reduction of Gene Flow • Mating is not random • The flow of genes does not spread throughout the entire population
Patterns of Evolution • There are different patterns in evolution. We will cover the following: • Divergent • Convergent • Co-evolution
Divergent • The process of two or more related species becoming more and more dissimilar • To diverge means to go or extend in different directions from a common point; branch out.
Adaptive radiation • This process in which one species gives rise to multiple species that exploit different niches is called adaptive radiation.
Convergent • When species of different ancestry begin to share analogous traits because of a shared habitat. • Analogous structures have the same function but do not come from a common ancestor
Co-evolution • Change in the genetic composition of one species (or group) in response to a genetic change in another. • So for example, an evolutionary change a plant, might affect the herbivore that eats the plant.
Homologous structures • Have different functions but share a common ancestor. Opposite of analogous structures.
Your test is on evolution and classification • KPCOFGS • Phylogenic tree • Dichotomous key • Evolution • Natural selection • Survival of the fittest • Darwin • Lamark – use and disuse theory • Stabalizing, disruptive, directional • Migration, mutation, genetic drift, natural selection • Founder effect, bottle neck effect • Co-evolution, divergent, convergent • Adaptive radiation • Homologous structures, analogous structures • Antiviral, antibiotic, pesticide, resistance
