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Transcript
• TEK: Analyze and evaluate how natural selection produces change in populations, not individuals.[7C] LEARNING TARGET: By the end of class today… I can analyze and evaluate how natural selection produces change in populations, not individuals… Natural Selection Mutations Recombination Gene Flow Genetic Drift What does this mean? Artificial Selection Non-Random Mating Isolation Evolution • Changes in a population over time. • Mechanisms of evolution – – – – – – – – Mutations Gene flow Genetic drift Natural Selection (survival of the “fittest”) Artificial Selection Recombination Non-Random Mating Isolation Mechanism of Evolution: Mutations Original Population Mechanism of Evolution: Mutations After Mutation Mechanism of Evolution: Mutations Many Generations Later Gene Flow • Genes move with individuals when they move (emigrate or immigrate) into and out of a population…and it changes the gene pool Genetic Drift • Genetic Drift – the random fluctuation due to chance occurrences alone • It is more significant in smaller populations • It increases the chance of any given allele becoming more or less prevalent when the number of individuals is small Non-Random Mating Original Population Blue = BB or Bb Red = bb x Non-Random Mating Many Generations Later Recombination & Genetic Shuffling As we learned in the genetics unit, recombination leads to genetic material being shuffled. This shuffling, along with sexual reproduction, leads to variation within populations. This variation leads to selection, which ultimately leads to evolution. What is the difference between artificial and natural selection? • Breeding organisms with specific traits in order to produce offspring with ideal traits is called artificial selection. (Intentional breeding for certain traits) A Goldendoodle (Golden retriever/ Poodle) Natural Selection • Natural selection is the idea that organisms with favorable/beneficial traits survive, reproduce, and pass those traits to the next generation. ENVIRONMENTALLY CONTROLLED • Organisms without these variations/traits are less likely to survive and reproduce. Darwin and Natural Selection • Charles Darwin (1809- 1882) He was an English scientist and it took him years to develop his theory of natural selection. • He began in 1831 at age 22 when he took a job as a naturalist on the English ship HMS Beagle, which sailed around the world on a five-year scientific journey. Darwin and Natural Selection • One of the things Darwin observed is that in nature, the traits of individuals vary in populations. • Then these variations are passed to offspring. • Darwin hypothesized that there was a force in nature that picked traits which are better for survival in a species. Darwin and Natural Selection • He also observed that individuals struggle to compete in changing environmental conditions. • What do individuals compete for? RESOURCES • Only some individuals survive the competition and live to produce offspring. ADAPTATIONS • Recall that an adaptation is any variation that aids an organism’s chances of survival in its environment. • Examples are: Thorns on plants Special colorings for an organism Enhanced night vision ADAPTATIONS • Some other structural adaptations are subtle. • Mimicry is a structural adaptation that enables one species to resemble another species. • In one form of mimicry, a harmless species has adaptations that result in a physical resemblance to a harmful species. ADAPTATIONS • Another subtle adaptation is camouflage, an adaptation that enables species to blend with their surroundings. • Because well-camouflaged organisms are not easily found by predators, they survive to reproduce. Darwin’s 5 points 1. Population has variations. 2. Some variations are favorable. 3. More offspring are produced than survive 4. Those that survive have favorable traits. 5. A population will change over time. NATURAL SELECTION • There are three different types of natural selection: stabilizing, directional, and disruptive. • Stabilizing selection is a natural selection that favors average individuals in a population. Evolution will not occur Middle sized Siberian Huskies are selected for NATURAL SELECTION • Directional selection occurs when natural selection favors one of the extreme variations of a trait. • This type of selection can lead to rapid evolution of a population. NATURAL SELECTION • In disruptive selection, individuals with either extreme of a trait’s variation are selected for. • This results in eventually having no intermediate form of a trait, and leading to two separate species. Natural Selection on Polygenic Traits • Shifts to middle range • Shifts to 2 extremes • Shifts to 1 extreme SPECIATION • The evolution of new species, a process called speciation. • This occurs when members of similar populations change so much from each other that they no longer interbreed to produce fertile offspring. SPECIATION • In nature, physical barriers can break large populations into smaller ones. • Geographic isolation occurs whenever a physical barrier divides a population and over time they change and become two different species. •Reproductive isolation… SPECIATION without a physical barrier • Some speciation occurs while the organisms still exist in the same area… •Reproductive Isolation •Behavioral, Temporal, Mechanical Speciation Northern population Early fox population Spreads northward and southward and separates Arctic Fox Different environmental conditions lead to different selective pressures and evolution into two different species. Southern population Gray Fox Adapted to cold through heavier fur, short ears, short legs, short nose. White fur matches snow for camouflage. Adapted to heat through lightweight fur and long ears, legs, and nose, which give off more heat. Types of Change • Divergent evolution is when species that are similar and closely related become increasingly different from each other. THEY DIVERGE This is also called Adaptive Radiation….because it has to do with ADAPTING to different environments and RADIATING out into different species. Types of Change • When distantly-related organisms evolve to become more similar, it is called convergent evolution. • Convergent evolution occurs when unrelated species occupy similar environments in different parts of the world. Also: Co-Evolution & Parallel Evolution Rate of Speciation • Current debate: Does speciation happen gradually or rapidly? Or both? – Gradualism – Punctuated equilibrium Gradualism Gradual change over long spans of time assume that big changes occur as the accumulation of many small ones develop over time. Punctuated Equilibrium • Rate of speciation is not constant – rapid bursts of change – long periods of no change – species undergo rapid change when they 1st bud from parent population Time