NameMy pts Pts Poss.Tot “My Pts” TPP Grade 3 Peppered Moth 10 170 4 Bill Nye 10 180 5 Bird Beak 15 195 Goal: Summarize the effects of the different types of natural selections on gene pools.
15.2 Section Objectives – page 404 Section Objectives Summarize the effects of the different types of natural selections on gene pools.
Section 15.2 Summary– pages 404-413 There are three different types of natural selection that act on variation: stabilizing, directional, and disruptive. Natural selection acts on variations Variations increase or decrease an organism’s chance of survival in an environment.
Section 15.2 Summary– pages 404-413 Stabilizing selection is a natural selection that favors average individuals in a population. Selection for average size spiders Normal variation Natural selection acts on variations
Section 15.2 Summary– pages 404-413 Natural selection acts on variations Directional selection occurs when natural selection favors one of the extreme variations of a trait. Normal variation Selection for longer beaks
Section 15.2 Summary– pages 404-413 Natural selection acts on variations In disruptive selection, individuals with either extreme of a trait’s variation are selected for. Selection for light limpets Normal variation Selection for dark limpets
Section 15.2 Summary– pages 404-413 Natural selection acts on variations Natural selection can significantly alter the genetic equilibrium of a population’s gene pool over time. Significant changes in the gene pool could lead to the evolution of a new species over time. (speciation)
Section 15.2 Summary– pages 404-413 Physical barriers can prevent interbreeding In nature, physical barriers can break large populations into smaller ones. Geographic isolation occurs whenever a physical barrier divides a population. A new species can evolve when a population has been geographically isolated.
Section 15.2 Summary– pages 404-413 The Evolution of Species When geographic isolation divides a population of tree frogs, the individuals no longer mate across populations.
Section 15.2 Summary– pages 404-413 The Evolution of Species The formation of a river may divide the frogs into two populations.
Section 15.2 Summary– pages 404-413 The Evolution of Species Over time, the divided populations may become two species that may no longer interbreed, even if reunited.
Section 15.2 Summary– pages 404-413 Mistakes during mitosis or meiosis can result in polyploid individuals. Parent plant (2n) Meiosis begins Nondisjunction Normal meiosis Normal gametes (n) Fertilization Zygote (3n) Abnormal gametes (2n) Fertilization Zygote (4n) Sterile plant New polyploid species A change in chromosome numbers and speciation
Section 15.2 Summary– pages 404-413 Speciation rates Gradualism is the idea that species originate through a gradual change of adaptations.
Section 15.2 Summary– pages 404-413 Speciation rates In 1972, Niles Eldredge and Stephen J. Gould proposed a different hypothesis known as punctuated equilibrium. This hypothesis argues that speciation occurs relatively quickly, in rapid bursts, with long periods of genetic equilibrium in between.
Section 15.2 Summary– pages 404-413 Speciation rates Loxodonta africana Elephas maximus Mammuthus primigenius Mammuthus Elephas Loxodonta Primelephas about 55 million years ago Ancestral species 6 5 4 3 2 1 0 Millions of Years Ago
Section 15.2 Summary– pages 404-413 Speciation rates Biologists generally agree that both gradualism and punctuated equilibrium can result in speciation, depending on the circumstances.
Section 15.2 Summary– pages 404-413 Patterns of Evolution Biologists have observed different patterns of evolution that occur throughout the world in different natural environments. These patterns support the idea that natural selection is an important agent for evolution.
Section 15.2 Summary– pages 404-413 Diversity in new environments When an ancestral species evolves into an array of species to fit a number of diverse habitats, the result is called adaptive radiation.
Section 15.2 Summary– pages 404-413 Adaptive radiation in both plants and animals has occurred and continues to occur throughout the world and is common on islands. Adaptive radiation is a type of divergent evolution, the pattern of evolution in which species that were once similar to an ancestral species diverge, or become increasingly distinct. Diversity in new environments
Section 15.2 Summary– pages 404-413 Possible Ancestral Lasan finch Amakihi Extinct mamo Crested honeycreeper Akialoa Akepa Akiapolaau Liwi Maui parrotbill Apapane Ou Grosbeak finch Palila Akikiki Niihau Kauai Oahu Lanai Molokai Maui Kahoolawe Hawaii Diversity in new environments
Section 15.2 Summary– pages 404-413 Diversity in new environments Divergent evolution occurs when populations change as they adapt to different environmental conditions, eventually resulting in new species.
Section 15.2 Summary– pages 404-413 Different species can look alike A pattern of evolution in which distantly related organisms evolve similar traits is called convergent evolution. Convergent evolution occurs when unrelated species occupy similar environments in different parts of the world.
Section 2 Check The fur of an Arctic fox turns white in the winter. Is this an example of natural selection? Why or why not? Question 1 IN: 1.32
Section 2 Check The answer is no. An individual cannot evolve a new phenotype (in this case, changing the color of its fur) within its lifetime in response to its environment. IN: 1.32
Section 2 Check Which type of natural selection does NOT favor the evolution of new species? Question 2 D. directional C. stabilizing B. disruptive A. divergent IN: 1.3
Section 2 Check The answer is C. Stabilizing selection reduces variation in a population. IN: 1.3
Section 2 Check Which of the following rarely affects a population’s genetic equilibrium? Question 3 D. disruptive selection C. gene flow B. lethal mutations A. genetic drift
Section 2 Check The answer is B. Organisms with lethal mutations do not survive. Therefore, organisms with lethal mutations cannot produce enough offspring to affect a population’s genetic equilibrium.
Section 2 Check Why are the Galapagos Islands rich in unique species of organisms? Question 4 D. The island species have been subjected to stabilizing selection. C. The island species have been subjected to increased gene flow. B. The islands are geographically isolated. A. The islands are an area exhibiting an abnormal number of mutations. IN: 1.36
Section 2 Check The answer is B. Geographic isolation has helped to keep the islands’ species unique. IN: 1.36
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