Chapter 21 & 23 PPT PDF

Chapter 21 How Evolution Works 陳炤杰 副教授 生物醫學暨環境生物學系 辦公室: N929，分機: 2696 E-mail:...

Chapter 21 How Evolution Works 陳炤杰 副教授 生物醫學暨環境生物學系 辦公室: N929，分機: 2696 E-mail: [email protected] Lecture Presentations by Nicole Tunbridge and © 2021 Pearson Education Ltd. Kathleen Fitzpatrick Figure 21.1a Figure 21.1a The Malaysian orchid mantis © 2021 Pearson Education Ltd. Figure 21.1b © 2021 Pearson Education Ltd.  Mantises illustrate three key observations about life: – Organisms are adapted for life in their biotic and abiotic environments – The many shared characteristics (unity) of life – The diversity of life Evolution refers to the process by which species accumulate differences from their ancestors as they adapt to different environments over time This definition is summarized by Darwin’s phrase descent with modification © 2021 Pearson Education Ltd. CONCEPT 21.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species Publication of The Origin of Species by Charles Darwin in 1859 started a scientific revolution—the era of evolutionary biology Darwin’s ideas developed gradually, through the influence of other’s works and his own travels Carolus Linnaeus (1707–1778) developed a nested classification system grouping similar species into increasingly inclusive categories He also developed the binomial format for naming species (for example, humans are Homo sapiens) © 2021 Pearson Education Ltd. Figure 21.2 © 2021 Pearson Education Ltd. Ideas About Change over Time Darwin drew from the study of fossils, remains or traces of organisms from the past Many fossils are found in sedimentary rock, which appears in layers called strata Archaeopteryx © 2021 Pearson Education Ltd. Lamarck’s Hypothesis of Evolution Jean-Baptiste de Lamarck (1744–1829) proposed two principles to explain evolutionary change – Use and disuse: body parts used extensively become larger and stronger, unused parts deteriorate – Inheritance of acquired characteristics: modifications acquired in one’s lifetime can be passed to offspring This mechanism is not supported by experimental evidence © 2021 Pearson Education Ltd. CONCEPT 21.2: Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life Darwin hypothesized that species from the mainland colonized and then diversified on the islands © 2021 Pearson Education Ltd. Figure 21.6 Three examples of beak variation in Galápagos finches Adaptations are inherited characteristics that enhance an organism’s survival and reproduction in specific environments. © 2021 Pearson Education Ltd.  Darwin proposed natural selection as an explanation for adaptation Natural selection is a process in which individuals with certain inherited traits tend to survive and reproduce at higher rates because of those traits Darwin wrote down his ideas in 1844, but did not publish out of concern they would cause an uproar He continued to compile supporting evidence In June 1858, Alfred Russel Wallace (1823–1913) sent Darwin a manuscript describing a nearly identical hypothesis of natural selection © 2021 Pearson Education Ltd.  Darwin viewed the history of life as a tree, with multiple branchings from a common trunk – Labeled branches represent groups of organisms living in the present day – Unlabeled branches represent extinct groups – A fork represents the most recent common ancestor of all lines of evolution branching from that point common ancestor © 2021 Pearson Education Ltd. Figure 21.8 – For example, living elephant species are similar because they split from a recent common ancestor – The extinction of seven older species helps explain the dissimilarity between elephants and their nearest living relatives, hyraxes and manatees © 2021 Pearson Education Ltd. Figure 21.9 Humans modify species through artificial selection, breeding only individuals with desired traits © 2021 Pearson Education Ltd.  Darwin drew two inferences from two observations – Observation #1: Members of a population often vary in their inherited traits – Observation #2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce © 2021 Pearson Education Ltd.  Inference #1: Individuals with inherited traits that increase survival and reproduction in an environment tend to produce more offspring than other individuals Inference #2: The unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations © 2021 Pearson Education Ltd.  Summary of key concepts: natural selection © 2021 Pearson Education Ltd.  For example, offspring may inherit a trait that helps them escape predators. Even slight advantages gradually accumulate in the population. In this way, organisms become better suited for life in their environment © 2021 Pearson Education Ltd. CONCEPT 21.3: Evolution is supported by an overwhelming amount of scientific evidence New discoveries continue to fill the gaps identified by Darwin in The Origin of Species Four types of data document the pattern of evolution – Direct observations – Homology – The fossil record – Biogeography © 2021 Pearson Education Ltd.  Direct Observations of Evolutionary Change 倒地鈴 欒樹 © 2021 Pearson Education Ltd. The Evolution of Drug-Resistant Bacteria The bacterium Staphylococcus aureus occurs on the skin or nasal passages of about one in three people  Certain strains, called methicillin-resistant S. aureus (MRSA), are pathogens that can cause potentially fatal infections (耐甲氧西林金黃色葡萄球菌) – Resistance to penicillin evolved in S. aureus by 1945, two years after it was first widely used – In recent decades, antibiotic resistance has spread faster than new antibiotics have been discovered © 2021 Pearson Education Ltd. Figure 21.14 Natural selection does not create new traits; it selects for traits already present in the population © 2021 Pearson Education Ltd. Homologous structures Related species can have characteristics that have an underlying similarity yet function differently. For example, the forelimbs of all mammals have the same arrangement of bones, but different functions © 2021 Pearson Education Ltd.  Vestigial structures are remnants of features that served a function in the organism’s ancestors – For example, snakes arose from ancestors with legs; the skeletons of some snakes retain vestiges of pelvis and leg bones 2021 Pearson Education Ltd. © 2018  Evolutionary trees are diagrams that reflect hypotheses about the relationships among groups Homologies form nested patterns on the tree Relatedness is determined by the recent common ancestor, not the proximity of groups on the tree Evolutionary trees are made using many different data sets, including both anatomical and DNA sequence data Similarities in such homologous genes are evidence of inheritance from a common ancestor © 2021 Pearson Education Ltd. Figure 21.17 © 2021 Pearson Education Ltd.  Convergent evolution is the evolution of similar, or analogous, features in distantly related groups through independent adaptation to similar environments © 2021 Pearson Education Ltd. The Fossil Record The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time – For example, the fossil record supported the DNA- based hypothesis that cetaceans are close relatives of even-toed ungulates Fossils can document important transitions, such as the transition from land to sea in the ancestors of cetaceans © 2021 Pearson Education Ltd. Figure 21.19 The ancestors of cetaceans © 2021 Pearson Education Ltd. Figure 21.20 The ancestors of cetaceans © 2021 Pearson Education Ltd.  Chapter 23 Microevolution 陳炤杰 生物醫學暨環境生物學系 辦公室: N929，分機: 2696 E-mail: [email protected] Lecture Presentations by Nicole Tunbridge and © 2021 Pearson Education Ltd. Kathleen Fitzpatrick  The medium ground finch (Geospiza fortis) is a seed-eating bird that inhabits the Galápagos Islands. © 2021 Pearson Education Ltd. Figure 23.2 In 1977, the population was decimated by a long period of drought: Of some 1,200 birds, only 180 survived. The surviving birds had larger, deeper beaks, indicating that this population of finches had evolved. © 2021 Pearson Education Ltd. What mechanisms can cause the evolution of populations? Natural selection acts on individuals, but only populations, not individuals, evolve Microevolution, the change in allele frequencies in a population over generations, is evolution at its smallest scale Three mechanisms cause allele frequency change: – Natural selection (adaptation to the environment) – Genetic drift (chance events alter allele frequencies) – Gene flow (transfer of alleles between populations) © 2021 Pearson Education Ltd. Figure 23.1b © 2021 Pearson Education Ltd. CONCEPT 23.1: Genetic variation makes evolution possible Genetic variation, variation in heritable traits, is a prerequisite for evolution by natural selection Gregor Mendel’s work on pea plants provided evidence of discrete heritable units (genes) Phenotype is the product of inherited genotype and environmental influences Natural selection can only act on variation with a genetic component © 2021 Pearson Education Ltd. Genetic Variation Genetic variation refers to the differences in genes or other DNA sequences among individuals Discrete characters or quantitative characters Coat color varies along a continuum and is influenced by multiple genes © 2021 Pearson Education Ltd.  At the gene level, genetic variation is quantified by the percentage of heterozygous loci in a population (average heterozygosity: fruit fly:14% for 13,700 loci) At the molecular level, genetic variation is quantified by comparing the nucleotide sequences of two or more individuals (fruit fly:1% for 180 million nucleotide) Nucleotide variability rarely results in phenotypic variation © 2021 Pearson Education Ltd. Sources of Genetic Variation New genes and alleles arise by mutation, gene duplication, or other processes Mutations can be caused by replication errors or exposure to certain types of radiation or chemicals Even a point mutation, change in a single nucleotide, can have significant impact on phenotype Sexual reproduction can produce genetic variation by recombining existing alleles In multicellular organisms, only mutations in cell lines that produce gametes are passed to offspring © 2021 Pearson Education Ltd. CONCEPT 23.2: The Hardy-Weinberg equation can be used to test whether a population is evolving Genetic variation is required for a population to evolve, but does not guarantee that it will A population is a group of individuals of the same species that live in the same area and interbreed Geographically isolated populations rarely exchange genetic material If populations are not isolated, individuals still usually only breed with members of their own population © 2021 Pearson Education Ltd. Figure 23.6 Caribou(馴鹿),one species, two populations © 2021 Pearson Education Ltd.  The gene pool consists of all copies of every allele at every locus in all members of the population A locus is fixed if all individuals in a population are homozygous for the same allele If there are two or more alleles for a locus, individuals may be homozygous or heterozygous Each genotype and each allele has a frequency in the population that can be calculated © 2021 Pearson Education Ltd.  Consider a population of 500 wildflowers with 320 red flowers (CRCR), 160 pink flowers (CRCW) and 20 white flowers (CWCW) To calculate genotype frequencies, divide the number of individuals of each genotype by the total number of individuals in the population – CRCR is 0.64 (320/500) 320 – CRCW is 0.32 (160/500) – CWCW is 0.04 (20/500) 20 160 © 2021 Pearson Education Ltd.  Allele frequencies can also be calculated for a population – For diploid organisms, the total number of alleles at a locus is the total number of individuals times two – Count two dominant alleles for each homozygous dominant individual and one for each heterozygote – The same logic applies for recessive alleles Calculate the number of copies of each allele – CR = (320 × 2) + 160 = 800 (p = 0.8) – CW = (20 × 2) + 160 = 200 (q = 0.2) The frequency of all alleles in a population will add up to 1, that is, p + q = 0.8 + 0.2 = 1 © 2021 Pearson Education Ltd. The Hardy-Weinberg Equation The Hardy-Weinberg equation describes the expected genetic makeup for a population that is not evolving at a particular locus If the observed genetic makeup of the population differs from expectations under Hardy-Weinberg, then the population may be evolving If a population is not evolving, genotype and allele frequencies will be constant from generation to generation Such a population is in Hardy-Weinberg equilibrium © 2021 Pearson Education Ltd. Figure 23.7 © 2021 Pearson Education Ltd. Figure 23.8 © 2021 Pearson Education Ltd.  If p and q represent the relative frequencies of the only two possible alleles in a population at a particular locus, then 基因型之比例 – where p2 and q2 represent the frequencies of the homozygous genotypes, and 2pq represents the frequency of the heterozygous genotype © 2021 Pearson Education Ltd. Try out 1 In peas, a gene controls flower color such that B = purple and b = white. The purple allele is dominant to the white allele. In an isolated pea patch, there are 36 purple-flowering plants and 64 white-flowering plants. Assuming Hardy-Weinberg equilibrium, what is the value of q for this population? A) 0.36 B) 0.64 C) 0.75 D) 0.80 © 2021 Pearson Education Ltd. Table 23.1 In real populations, allele and genotype frequencies often do change over time when one or more of the conditions are not met. © 2021 Pearson Education Ltd. Try out 2 A locus that affects susceptibility to a degenerative brain disease has two alleles, A and a. In a population, 16 people have genotype AA, 92 have genotype Aa, and 12 have genotype aa. Is this population evolving? Explain. © 2021 Pearson Education Ltd. CONCEPT 23.3: Natural selection, genetic drift, and gene flow can alter allele frequencies in a population Three major factors alter allele frequencies directly and bring about most evolutionary change: – Natural selection – Genetic drift 基因漂變 – Gene flow Only natural selection can cause adaptive evolution, a process in which traits that enhance survival or reproduction increase in frequency over time © 2021 Pearson Education Ltd. Genetic Drift The smaller the sample, the greater the chance of random deviation from a predicted result Genetic drift is a process in which chance events cause allele frequencies to fluctuate unpredictably from one generation to the next Genetic drift tends to reduce genetic variation through the random loss of alleles © 2021 Pearson Education Ltd. Figure 23.9 Chance plays a major role © 2021 Pearson Education Ltd. The Founder Effect 先驅效應，創始者效應 The founder effect occurs when a few individuals become isolated from a larger population Allele frequencies in the smaller founder population are different from those in the parent population – For example, genetic drift could occur if a few individuals are indiscriminately blown to a new island by a storm © 2021 Pearson Education Ltd. The Bottleneck Effect 瓶頸效應 The bottleneck effect occurs when there is a drastic reduction in population size due to a sudden change in the environment Understanding the bottleneck effect can increase understanding of how human activity affects other species (瀕臨絕種生物，如雲豹、石虎) © 2021 Pearson Education Ltd. Case Study: the Greater Prairie Chicken © 2021 Pearson Education Ltd. Gene Flow Gene flow consists of the movement of alleles among populations Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen) Gene flow tends to reduce variation among populations over time Gene flow affects adaptation to local environments – Unbanded snakes are better camouflaged on islands – Ongoing migration of banded snakes from the mainland population maintains disadvantageous alleles for banding pattern on the islands © 2021 Pearson Education Ltd. Figure 23.12 © 2021 Pearson Education Ltd. CONCEPT 23.4: Natural selection is the only mechanism that consistently causes adaptive evolution Evolution by natural selection involves both chance and “sorting” – New genetic variations arise by chance – Beneficial alleles are “sorted” and favored by natural selection Only natural selection consistently increases the frequencies of alleles that provide reproductive advantage © 2021 Pearson Education Ltd. Directional, Disruptive, and Stabilizing Selection There are three ways in which natural selection can alter the frequency distribution of heritable traits: – Directional selection favors individuals at one extreme end of the phenotypic range – Disruptive selection favors individuals at both extremes of the phenotypic range – Stabilizing selection favors intermediate variants and acts against extreme phenotypes © 2021 Pearson Education Ltd. Figure 23.13 © 2021 Pearson Education Ltd. Sexual Selection Sexual selection is a process in which individuals with certain heritable traits are more likely to obtain mates than other individuals of the same sex It can result in sexual dimorphism, a difference in secondary sexual characteristics between the sexes – For example, males and females may differ in size, color, ornamentation, and behavior © 2021 Pearson Education Ltd. Figure 23.15 Sexual dimorphism in peacock and peahen Intersexual selection (mate choice) occurs when individuals of one sex (usually females) are choosy in selecting their mates © 2021 Pearson Education Ltd. Figure 23.16 The “good genes” hypothesis proposes that females select males with traits that are related to their genetic quality. © 2021 Pearson Education Ltd. Balancing Selection Balancing selection preserves variation at some loci by maintaining stable frequencies of two or more phenotypes by – Frequency-dependent selection – Heterozygote advantage In frequency-dependent selection, the fitness of a phenotype depends on how common it is – For example, frequency-dependent selection results in approximately equal numbers of “right-mouthed” and “left-mouthed” scale-eating fish © 2021 Pearson Education Ltd. Figure 23.17 © 2021 Pearson Education Ltd. Figure 23.13 © 2021 Pearson Education Ltd. Heterozygote Advantage Heterozygote advantage occurs when heterozygotes have a higher fitness than both kinds of homozygotes For example, the deleterious sickle-cell allele is maintained at relatively high frequencies in some regions due to heterozygote advantage Heterozygotes experience few harmful effects, but are more likely to survive malaria than homozygotes Where malaria is common, heterozygote advantage increases the frequency of sickle-cell alleles © 2021 Pearson Education Ltd. Figure 23.18b Make Connections: The Sickle-Cell Allele “Heterozygote protection” maintains a pool of alleles that could be beneficial if the environment changes Infected mosquitoes spread malaria. Frequencies of the sickle-cell allele 3.0–6.0% 6.0–9.0% 9.0–12.0% 12.0–15.0% >15.0% Distribution of malaria This child has sickle-cell disease, Heterozygotes are more likely to survive malaria. a genetic disorder. Evolution in Populations © 2021 Pearson Education Ltd.