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AP Biology

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AP BIOLOGY • EVOLUTION ESSAY EXAM (RAVEN CHAPTERS 21, 22, 23) 1. Charles Darwin proposed that evolution by natural selection was the basis for the differences that he saw in similar organisms as he traveled and collected specimens in South America and on the Galapagos Islands. Explain the theory of evolution by natural selection as presented by Darwin. - variation in populations - adaptations: differences may enable some individuals to out-compete others - differential survival: individuals with more favorable traits will be “selected” - competition for food, nesting sites, mates, escape predators, survive disease/parasites - survivors are then able to reproduce more and pass on favorable traits to their offspring. - individuals with favorable traits will make up a greater percentage of the population in the next generation. NO CREDIT for mentioning genetics or genes. Darwin did not know about genes. 2. Evolution by natural selection has been able to explain both the unity and diversity of life on Earth. Discuss how natural selection explains the following phenomenon and cite an example for each: a. Mimicry - Population 1 has an adaptation that enables individuals to survive and reproduce - Population 2 originally contained variations that included some similarity to Population 1. This served as an adaptation & these individuals were afforded the same advantage as those in Population 1. Mimics are therefore selected for and are able to survive and reproduce more passing on the trait - Example: warning coloration of monarch butterflies or poisonous snakes b. Convergent evolution - “similar solutions to similar problems”: analogous structures - similar adaptations that enable unrelated organisms to be successful but are not due to a recent common ancestor - Example: wings on birds, insects, bats c. Parallel evolution

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AP Biology

- parallel evolution: superficial similarity of species in similar biomes that lie in vastly different regions of the world - “similar solutions to similar problems in same ecological role”: adaptations that enable an organism to be successful in a particular niche are repeated in similar environments in different regions - traits that make individuals successful in certain ecological roles (i.e., burrower, insectivore, chasing predator) will be selected for even if they live in vastly different regions. - Example: marsupial mammals and placental mammals 3. Compare and contrast artificial selection and natural selection. Explain how the former was useful to Darwin in his thinking about evolution. Cite examples of artificial selection. - artificial selection is human-created evolution; intentional selection - humans are the selection agent: they select the traits in a species that they want to propagate; humans choose the matings and therefore determine which individuals are successful. - artificial selection does not produce individuals that are adapted to the environment, but rather adapted to human use. - natural selection is based environmental selection factors. Adaptations bring about successful in a natural setting. - both exert a selection pressure on a species. - artificial selection enabled Darwin to see that traits are passed from parent to offspring & that traits could accumulate in a population if individuals bearing those traits are allowed to reproduce selectively. - Example: dogs, pigeons (Darwin’s direct experience), Brassicae (cole) crops, many other agricultural examples. 4. In terms of climate and geology, Charles Darwin noted that Galapagos Islands are nearly identical to the Canary Islands. Darwin was struck, however, by the fact that the Canary Islands, just off the coast of Africa (200km or 120 miles), contain very few unique species. Whereas the Galapagos Islands, over 800km (~500 miles) off the coast of South America, are home to scores of unique species, found nowhere else in the world. Give a concise evolutionary explanation for why remote islands would give rise to unique species, while those relatively close to mainland contain few if any species not found on the mainland. - remote islands are isolated - strong selection pressure to adapt to the environment or not survive. - adaptive radiation colonizing new habitats/niches; first colonizers fill unoccupied niches - founder effect & genetic drift; no gene flow - geographic isolation in allopatric species - nearby islands share migration with mainland

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- gene flow - migration may mean island population & mainland share gene pool - may have similar selective pressures as mainland - similar niches on mainland & island will be populated by same species so they will experience similar selective pressures therefore few opportunities for the evolution of new or distinct species 5. Explain how the fossil record supports the principle of evolution by natural selection. - many extinct species resemble modern species but have slight differences in traits - fossils show change over time - modern species have survived due to variations in traits – adaptations -- that allowed them to be more competitive 6. Much of the power of the theory evolution is its ability to provide a sensible framework for understanding the diversity of life. a. The illustration below shows the forelimbs of a variety of mammals. Describe the diagram and explain how this serves as evidence for evolution by natural selection. - homologous traits - same bones in each structure even though they serve different functions - differences in the structures are evidence of adaptation to different environments - similarities in the structures are evidence of common ancestry b. The illustration below shows the skeleton of a whale. Describe the diagram and explain how the highlighted structure serves as evidence for evolution by natural selection. - vestigial structure - remnants of pelvic bones - pelvic bones are only necessary for animals that have legs - evidence that whales descended from land mammals 7. Although individuals who are homozygous for the sickle-cell allele (HsHs) often die at a young age, the sickle-cell allele (Hs) is common in populations living in areas where malaria is prevalent. a. Briefly explain why the sickle-cell allele (Hs) is so common in regions where malaria is found. - heterozygote advantage

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- individuals homozygous normal (HbHb) are more susceptible to dying from malaria - individuals homozygous sickle-cell (HsHs) are more susceptible to dying from sickle cell disease - heterozygotes: malaria parasite is killed when cells sickle, so heterozygotes are less susceptible to malaria and do not have as crippling a case of sickle cell disease b. There are many diseases in which the homozygous recessive genotype is lethal at a young age. If these individuals never reproduce then why does the mutant allele persist in the population? - the recessive allele is hidden in the heterozygote, so they serve as a reservoir - the recessive allele is not selected against in the heterozygote since it does express phenotypically 8. In class, we discussed the manes of male lions as an example of sexual selection. As noted, female lions tend to chose males with large, dark manes as mates. a. Why are such manes considered examples of sexual selection rather than examples of other forms of natural selection? Be brief but specific. - manes don’t benefit the males directly; don’t help them hunt, survive, etc. - a mane is, in fact, uncomfortable to the individual possessing it - its main role is to promote reproductive success: finding a mate - doesn’t help individual survive; helps individual reproduce b. The selective pressure on male lions should be obvious. Those who do not inherit genes that help them to produce large, dark manes are less likely to breed. Explain, however, the selective pressure on the lioness in terms of instinctive behavior in mate choice by describing the forces that cause them to select for such males. - females pick mates on an instinctive preference - if this instinctive preference has the female choosing a mate with large dark mane, she will automatically be choosing a fit mate, with a high testosterone level and probably with a high sperm count - that instinctive behavior will be rewarded with lots of offspring (because of high sperm count) and pretty good protection because the male is pretty fit. - for females who instinctively choose males with small light manes that behavior will be penalized with higher mortality rates in cubs (from less fit male) and fewer offspring (from a male with a lower sperm count). - automatic system that tends to pick for behaviors that automatically result in reproductive fitness

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- NO CREDIT for female “wants” to find a fit male or female “wants” to provide for her offspring, or female sees dark mane and “knows” the male has high testosterone level. 9. Molecular biology has given us the tools to test evolutionary theory beyond what could even be imagined in Darwin’s day. Describe and explain examples of evidence which molecular biology has discovered that: a. supports the understanding that clusters of species share a recent common ancestor, and - similar sequences in genes in closely related species - we assume that DNA changes (mutation) at a constant rate - the more similar the sequence the more closely related. - Example: compare amino acid sequence of hemoglobin in vertebrates or Cytochrome C across a broad array of species b. supports the understanding that all life on earth arose from a single common ancestor. - all of life on Earth uses DNA as its genetic information - universal code - many key genes and their protein products are well-conserved across very diverse organisms - Example: Cytochrome C or other proteins involved in respiration 10. Are natural populations ever in Hardy-Weinberg equilibrium? List and explain each of the assumptions of Hardy-Weinberg equilibrium and compare each with the actual situation in natural populations. Cite examples to support your argument. - No, natural populations are rarely (never?) in H-W equilibrium. - infinitely large populations - no such thing…population growth is finite - no selection - the environment exerts a selective force (predators, parasite, disease, competition) - no mutation - errors in replication happen at a constant rate - random mating - sexual selection exists - no gene flow - immigration & emigration usually happens

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