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Unit 4: Evolution

Unit 4: Evolution . Definitions:. Evolution the relative change in the characteristics of populations that occurs over successive generations Adaptation a particular structure, physiology or behaviour that helps an organism survive and reproduce in a particular environment Variation

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Unit 4: Evolution

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  1. Unit 4: Evolution

  2. Definitions: • Evolution • the relative change in the characteristics of populations that occurs over successive generations • Adaptation • a particular structure, physiology or behaviour that helps an organism survive and reproduce in a particular environment • Variation • differences among traits occur among members of the same species. Therefore no two individuals are exactly alike • these variations are passed on to the next generation

  3. Peppered Moth P. 664-665 • Industrial melanism • when air pollution levels are high, the trees are dark. This “favours” the survival of dark-winged moths • when air pollution levels are low, the trees are light. This “favours” the survival of light-winged moths • Survival of the “fittest” • wing colour supports the camouflage of the moth and allows it to survive to reproduce.

  4. Natural selection Pp 347-349 • process in which characteristics of a population of organisms change because individuals with certain inheritable traits survive specific local environmental conditions • there must be diversity within a species for this to occur • the environment exerts a selective pressure on a population, selecting individuals with certain characteristics and eliminating others

  5. Artificial selection • a breeder selects desired characteristics in an organism • Eg: Dog breeders

  6. Charles Lyell P. 655 • developed theory of uniformitarianism • said that all geological processes operated at the same rates in the past as they do today • important because it indicated the world was much older than 6000 years, and that slow processes happening over long periods of time could result in substantial changes

  7. Thomas Malthus P. 656 • plant and animal populations grew faster than their food supply • eventually a population is reduced by starvation, disease or war

  8. Alfred Wallace P 657 • wrote Darwin with essentially identical theory of evolution • forced Darwin into publishing theory of evolution

  9. Jean Baptiste Lamarck P. 651 • presented first theory that discussed the possibility of evolution • believed that organisms have an imaginary force or desire to change themselves for the better • believed in the idea of inheritance of acquired characteristics • Although this theory has been rejected Lamarck’s main contribution was to show that evolution is adaptive, and that the diversity of life is the result of adaptation

  10. Georges Cuvier P. 650 • developed the science of paleontology • realized the Earth’s history was recorded in the fossil record • recognized that extinction was a fairly common occurrence • strongly opposed to the theory of evolution

  11. Darwin • when Darwin observed living armadillos and the fossils of ancient armadillo-like creatures in the same location, He began to wonder why one had survived and the other had not. He would later conclude that one form had evolved from the other • while exploring the Galapagos Islands, he noted slight variations among similar species of organisms from island to island • 14 species of finch that were similar to a species of finch found on the mainland • The notable difference in finches lay in the shape of their beaks. • different beak shapes were adaptations for eating a certain kind of food characteristic of the various geographic location

  12. Darwin assumed that these different species had evolved from a single ancestral mainland species • started to formulate ideas about evolution • worked out the process of natural selection in 1838 • Published 21 years later (pushed by Wallace)

  13. Theory of Natural Selection • 1. Overproduction • the number of offspring produced by a species is greater than the number that can survive, reproduce and live to maturity • 2. Struggle of existence (competition) • because of overproduction, organisms of the same species, as well as those of different species, must compete for limited resources such as food, water and a place to live • 3. Variation • differences among traits occur among members of the same species. Therefore no two individuals are exactly alike these variations are passed on to the next generation • 4. Survival of the fittest (natural selection) • those individuals in a species with traits that give them an advantage (i.e., are well-adapted to their environment) are better able to compete, survive and reproduce. All others die without leaving offspring since nature selects the organisms which survive, the process is called natural selection • 5. Origin of new species (speciation) • over numerous generations, new species arise by the accumulation of inherited variations when a type is produced that is significantly different from the original, it becomes a new species

  14. Mendel - work built upon by later scientists to reveal: P 675 • there is MUCH genetic variation within populations • variations can arise through mutations and are inheritable • evolution, therefore, depends on both random genetic mutations (which provide variation) and • mechanisms such as natural selection

  15. Modern Evidence of Evolution • Fossil Record P 659 • The fossil record shows us: • the earliest organisms were small and simple in structure • over millions of years organisms became larger and more complex • the number of different kinds of organisms has increased over time • many species of organisms have disappeared and have been replaced by new and different species • The fossil record provides evidence of constantly changing life forms.

  16. Biogeography P 663-664 • study of the geographical distribution of species (continental drift) • isolationis a key factor in the evolution of species

  17. 1) Geographic isolation • occurs when a single breeding population is divided by a geographic boundary • e.g.,Canislupus beothicus • barriers include: • mountain ranges • bodies of water • barriers created by humans • gene flow between the isolated group and the main population ceases • different adaptations of populations in the separate environments, different gene frequencies within the separate populations and different mutations within the population • may all allow the population to become so different that interbreeding is impossible

  18. 2) Reproductive isolation • may occur because of geographic isolation • occurs when organism in a population can no longer mate and produce offspring, even following the removal of the geographic barriers • factors that contribute to reproductive isolation include: • differences in mating habits • courtship patterns • seasonal differences in mating (very few species can mate and reproduce at any time) • inability of the sperm to fertilize eggs

  19. Comparative Anatomy (homologous, analogous and vestigial structures) P 664-665 • organisms with similar structures evolved from a common ancestor becomes increasingly obvious. • Eg: flipper of a seal, the leg of a pig, the wing of a bat, and the human arm all have the same basic structure and the same pattern of early growth.

  20. 1) Vestigial organs • Def: small, incomplete organs with no apparent function • provide evidence of ancestry • e.g., snakes once had legs

  21. 2) Analogous structures • similar functions but different anatomically (insect/bird wings) • good indicators that these organisms didn’t come from common ancestors

  22. Comparative Embryology P 665 • Embryology is the study of organisms in the early stages of development. During the late 1800s, scientists noted a striking similarity between the embryos of different species (see page 683, Nelson). • At a later date, biologists suggested that the similarity of the embryos was due to their evolution from a common ancestor. This doesn’t mean that birds necessarily evolved from reptiles, or mammals from birds, but rather that the young forms of these organisms resemble the young of related species. • In a broad sense, there is a theory that every organism repeats its evolutionary development in its own embryology. • Scientists believe that many of the structures in an embryo are similar to those found in common ancestors

  23. Heredity P 666 • Mendel’s laws explain many variations Since the laws of inheritance and the science of genetics are more clearly understood than in Darwin’s time, the variations in organisms required for natural selection to occur can be explained

  24. Molecular Biology P 666-667 • evolutionary relationships among species are reflected in their DNA • the closeness of species can be determined by comparing DNA patterns • http://www.youtube.com/watch?v=IFACrIx5SZ0&safety_mode=true&persist_safety_mode=1&safe=active • DNA similarity reveals a common ancestor also shows that all life forms on earth are related, to some extent, to the earliest organisms

  25. How to date a fossil P 662 • the oldest layers are the ones laid down first and, therefore, are found at the bottom of the site • the younger layers, added later, are on top since fossils form along with a given layer of sedimentary rock, the relative ages of the fossils can also be determined • The oldest will be on the bottom; the youngest will be on the top • It takes about 1000 years to form 30 cm of sedimentary rock

  26. Absolute dating provides a much more accurate method of determining a fossil’s age via radioactive dating techniques. • A radioactive isotope has an unstable nuclear structure, and will break down, releasing particles and energy. • The breakdown often results in a more stable element. • Radioactive dating involves measurements of the decay of radioactive isotopes such as: • potassium-40, which becomes argon-40 • uranium-238, which changes to lead-206 • carbon-14, which becomes nitrogen-14

  27. For example, if a rock contains thorium 232 and lead 208 in equal amounts, then one half of the original thorium 232 has decayed; • one half-life has passed and the rock must be 14 billion years old

  28. Nucleic Acid evidence for evolution Pp666-667 • Cytochrome C • protein found in mitochondria • amino acid sequence is so similar among organisms that it can be used to indicate relatedness • e.g., chimps and rhesus monkeys differ by one amino acid; chimps and horses by 11 • the longer the period of time since an organism evolved from a simple ancestor,the greater the number of differences in the nucleotide sequences for the cytochrome c gene • http://www.youtube.com/watch?v=W-pc_M2qI74&feature=related&safety_mode=true&persist_safety_mode=1

  29. Hardy-Weinberg law Pp 681-686 • Gene pool - the entire genetic content of a population • If all other factors remain constant, the gene pool will have the same composition generation after generation. • This stability is called genetic equilibrium. • Only if that equilibrium is upset can the population evolve.

  30. The principle can be expressed mathematically by the formulae: • p2 + 2pq + q2 = 1 • and p + q = 1 • where • p = frequency of dominant allele • q = frequency of recessive allele • If the values for p and q are known, this equation can be used to calculate the frequency of all three genotypes, PP, Pq, and qq. • If the frequencies of the three genotypes are known, the frequencies of the alleles can be calculated.

  31. The conditions under which no change in the gene pool will occur are: • 1)large populations. This condition is necessary to ensure that changes in gene frequencies are not the result of chance alone • 2) random mating. • 3) no mutations • 4) no migration. No new genes enter or leave the population • 5) equal viability, fertility and mating ability of all genotypes (i.e., no selection advantage)

  32. Example: • Consider a simple situation - one gene with two alleles, A and a. • Thegenotypes that might be found in a large population will be AA, Aa and aa. • In mathematical terms, the frequencies with which the alleles will occur must add up to one (and so must the frequencies of the genotypes) • if the dominant allele, A, is found in 70% of the population (i.e., has a frequency of 0.7), • the recessive allele will have a frequency of 1 - 0.7 = 0.3, or 30%.

  33. The expected frequencies of the 3 possible genotypes can be calculated with a Punetsquare, or with the Hardy-Weinberg equation: • Sperm______________ • A (0.7) A (0.3)________ • A(0.7) AA (0.49) Aa (0.21)______ • a (0.3) Aa (0.21) aa (0.09)______ • Eggs

  34. The equation predicts that the frequencies of the 3 genotypes possible in the next generation will be: • p2 + 2pq + q2 = 1 • (0.7)2 + 2(0.7 x 0.3) + (0.3) = 1 • Genotypes: 49% AA; 42% Aa; 9% aa • Given this distribution of genotypes, it’s possible to predict the frequency of the A and a alleles in the population: • F1 generation 0.49 AA ; 0.42 Aa; 0.09 aa • potential gametes A A ; A a; a a • A = 0.49 + 0.21 = 0.7 • a = 0.21 + 0.09 = 0.3

  35. Problem: Suppose a recessive genetic disorder occurs in 9% of the population. Whatpercentage of the population is heterozygous, or carriers, of the disorder? • a = 0.09 = q2 ; q = 0.3 • AA = ? = p2; 1 - q = p; 1 = 0.3 = 0.7 • p2 + 2pq + q2 = 1 • (0.7)2 + 2(0.7 x 0.3) + (0.3) = 1 • 0.49 + 0.42 + 0.9 = 1

  36. The Hardy-Weinberg law: • compares natural populations with an ideal situation; such comparisons are a measure of change • In nature, allele frequencies are not constant and populations do change over time, or evolve • it shows that meiosis and sexual reproduction by themselves do not cause populations to change • Merely recombining genes does not change allele frequencies in a gene pool • Other factors must be at work

  37. Mutations P 688 • may provide new alleles in a population and, as a result, may provide the variation required for evolution to occur • if a mutation provides a selective advantage it may result in certain individuals producing a disproportionate number of offspring as a result of natural selection

  38. Genetic Drift P 689 • in small populations the frequencies of particular alleles can be changed by chance alone • the smaller the population the less likely the parent gene pool will be reflected in the next generation

  39. Bottleneck effect p. 690 • as a result of chance certain alleles are over represented and others are under represented in the reduced population • genetic drift then follows and the genetic variation in the surviving population is reduced • eg • Northern elephant seal; Hunting reduced population to as few as 20 individuals. The population today has reduced genetic variation as a result.

  40. Founder effect p. 691 • when a small number of individuals colonize a new area the chances are high that they do not contain all the genes represented in the parent population • eg • NL moose: since these founders are in a new environment, they will experience different selection pressure

  41. Gene Flow p 692 • the movement of new alleles into a gene pool • can reduce genetic differences between populations

  42. Non-random Mating p. 692 • 1) inbreeding • 2) self-fertilization • 3) assortativemating (choosing mates with a similar phenotype) • This is the basis for artificial selection e.g., breeding dogs

  43. Natural Selection p. 693 • some individuals in a population will leave more offspring than others due to selective pressures • 1) Stabilizing selection favours an intermediate phenotype and acts against extreme variants e.g., baby weights are between 3 and 4 kg • 2) Directional selection favours the phenotypes at one extreme over another. • Common during periods of environmental change e.g., in the wild budgies are usually green • 3) Disruptive (diversifying) selection takes place when extremes of a phenotypic range are favouredrelative to intermediate phenotypes. • As a result, intermediates will be eliminated from the population

  44. Sexual Selection p. 695 • characteristics used in sexual selection may not be adaptive in the sense that they help an individual survive. • E.g., peacock tail However, they may increase the chances of being chosen as a mate and therefore of passing genes along to the next generation

  45. Biological barriers to reproduction may contribute to speciation • Biological barriers: • 1) Pre-zygotic barriers p.709 • either impede mating between species or prevent fertilization of the ova if individuals from different species attempt to mate • 2) Behaviouralisolationism • bird song, courtship rituals, pheromones ... species-specific signals • 3) Habitat isolation • because of differing habitats, species may not encounter each other • 4) Temporal isolation p 710 • differences in times for mating (season, year, time of day) • 5) Mechanical isolation • anatomically so different that mating is impossible • 6) Gameticisolation • gametes of different species will not fuse

  46. Post-zygotic barriers P 710 • when the sperm of one species successfully fertilizes the ovum of another and a zygote is produced, these barriers prevent the hybrid from developing into normal, fertile individuals • Hybrid inviability • genetic incompatibility of the interbred species may stop development of the hybrid zygote • Hybrid sterility p 711 • hybrid is sterile e.g., donkey + horse = mule, which is usually sterile • Hybrid breakdown • 1st hybrid generation is viable and fertile. Subsequent offspring of hybrids are sterile or weak • http://www.youtube.com/watch?v=vJFo3trMuD8

  47. Convergent and divergent evolution P 721 • Divergent evolution • is adaptive radiation (homologous structures will be present between species) • Convergent evolution • occurs when the environment selects similar adaptations in unrelated species • If the environments are similar, it is logical to assume that some of the same kinds of traits would be favored in the different populations • (Analagousstructures will be present among species) • E.g., • Wings - birds, bats, bees • fins/streamlined shape - dolphins and sharks • eye structure - humans and octopus

  48. The process of coevolution P 722 • This process of joint evolution of two or more species is called coevolution. Flowering plants and insects, predator prey relationships, parasites and their hosts • http://www.youtube.com/watch?v=WeuQfToa254&feature=PlayList&p=6362D791829F413A&playnext_from=PL&index=54&playnext=3

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