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Ch. 22: Darwinian View of Life, Ch. 23: Evolution of Populations - Coggle…

- - - - Primary mission of the voyage was to chart stretches of the South American coast that were poorly known to Europeans.
        
        Observed and collected thousands of plants and animals from South America.
        
        Noted plants and animals in temperate regions of South America more closely resembled those living in the South American tropics than those found in temperate regions of Europe. AND the fossils found resembled the living organisms of South America even though they were different.
      - Darwin read Lyell's Principles of Geology during the voyage.
        
        Experienced a violent earthquake on the coast of Chile- observed the rocks had been thrust upward several meter- able to view fossils in the sedimentary rock.
        
        Finding fossils of the ocean high in the Andes- Darwin reasoned the rocks containing fossils must have been raised there by many similar earthquakes = the Earth was not only a few thousand years old.
      - The Galápagos
        
        The Galápagos is a group of volcanic islands west of South America.
        
        Most of Darwin's studies happened on the Islands.
        
        He collected many similar, but different species of birds. Some were unique to individual islands, while others were found on multiple islands.
        
        Even the animals unique to the islands resembled species on the nearby mainland of South America.
        
        Darwin hypothesized that species from the mainland colonized and then diversified on the islands.
        
        Darwin's Focus on Adaptation
        Adaptations- inherited characteristics that enhance an organism's survival and reproduction in specific environments.
        
        Perceived that new species could arise from ancestral forms through gradual accumulation of adaptations = Galápagos finches
        
        Proposed natural selection as an explanation for adaptation.
        Natural selection- process in which individuals with certain traits tend to survive and reproduce at higher rates because of those traits.
        
        In 1858, Alfred Wallace sent Darwin his manuscript with an identical hypothesis of natural selection.
        
        Wallace ended up submitting his book for publication before Darwin, but because of Darwin's extensive studies, Wallace thought Darwin should be known as the main architect of natural selection.
        
        Charles Darwin published his bok in 1859. Within a decade, most scientists were convinced that life's diversity is the product of evolution.
  - - - Darwin used descent with modification to describe his view of life. Evolution was never a word he used.
        Unity of life- all organisms are related by descent from a common ancestor that lived in the past.
        Diversity of life- as descendants of that ancestral organism lived in various habitats, they gradually accumulated diverse modifications (adaptations).
        
        Led to Darwin's theory that evolution is a process in which both descent (shared ancestry resulting in shared characteristics) and modification (accumulation of differences) are observed.
      - Darwin's Tree
        
        Reasoned descent with modification eventually led to the rich diversity of life we see today.
        
        Viewed history of life as a tree- with multiple branching's from a common trunk (common ancestor)
        -Labeled branches- groups of organisms living in the present day
        -Unlabeled branches- extinct groups
        -A fork- represents the most recent common ancestor of al lines of evolution branching from that point. Become different species when they can no longer reproduce with one another.
        
        Darwin thought that the branching process, along with past extinction events could explain the large morphological gaps that may exist between related groups of organisms.
        
        Ex. Elephant species- the extinction of seven older species helps explain dissimilarity between elephants and their nearest living relatives, hyraxes and manatees.
    - - Artificial Selection
        
        Artificial selection- breeding only individuals with desired traits.
        -Humans modify species of crops, livestock animals, and pets. They often bear little resemblance to their wild ancestors.
        
        Darwin argued similar process occurs in nature.
        
        Darwin drew two inferences from two observations:
        
        Observation 1: Members of a population often vary in their inherited traits.
        Ex. Asian ladybird beetles
        Observation 2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce.
        Ex. Spore cloud
        Inference1: 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 favorable traits in the population over generations.
        
        Darwin saw a connection between natural selection and the capacity of organisms to "over reproduce".
        
        Made this connection after reading Malthus' writings about the capacity of human populations to increase faster than critical resources.
        
        Darwin recognized this capacity in all species - carrying capacity
        
        Only a fraction of offspring complete development and reproduce; the rest are starved, eaten, unmated, diseased or intolerant of physical conditions.
        
        If advantageous traits increase the number of offspring that survive and reproduce, then they will appear at higher frequency in the next generation.
        Ex. offspring may inherit a trait that helps it escape predators or obtain food.
        
        Natural selection by predators, lack of food, or adverse conditions can increase the proportion of favorable traits in the population.= organisms become better suited for life in their environment.
      - Natural Selection: Main Ideas
        
        Natural selection- individuals with certain heritable trats survive and reproduce at a higher rate than others.
        
        Natural selection increases the frequency of adaptations that are favorable in an environment.
        
        If environment changes, natural selection ay drive adaptation to new conditions-giving rise to new species.
        
        Individuals do not evolve; it is the POPULATION that evolves over time.
        
        Natural selection can only increase or decreases heritable traits that are variable in a population.
        
        Environment varies from place to place and over time favorable traits vary with the environment.
- - - - Natural selection in response to introduced species- How population numbers are kept in check. Adaptations to help efficiently fee on primary food sources.
        Ex. Soapberry bugs most effectively feed when beak length is closely matched to seed depth within a fruit plant.
        
        In S. Florida- feed on balloon vines with large fruit; have long beaks.
        
        In C. Florida- feed on introduced golden rain tress with smaller fruit; have shorter breaks. (Evolution occurred in less than 35 years.)
        Beaks evolved depending on which seeds were there primary food source.
    - - Evolution of drug-resistant bacteria- methicillin-resistant Staphylococcus aureus (MRSA)
        
        Penicillin first used in 1943=Penicillin resistance by 1945.
        
        Methicillin, was introduced in 1959=methicillin resistance by 1961.
        Methicillin inhibits an enzyme that produces cell walls. MRSA can use different enzymes = MRSA increases in the presence of methicillin.
        New antibiotic "teixobactin" shows promise for treating resistant pathogens.
  - - - Characteristics shared by many species= deep ancestral past.
        
        Homologies evolved more recently are shared within smaller groups.
      - Evolutionary Trees
        
        Evolutionary trees- diagrams that reflect hypotheses about the relationships among groups.
        
        Relatedness is determined by the recent common ancestor, not the proximity of groups on the tree.
        
        Made using different data sets, both anatomical and DNA sequence data
    - - Organisms that are closely related share characteristics because of common descent, distantly related organisms resemble one another due to convergent evolution.
        Convergent Evolution- evolution of similar (analogous) feature in distantly related groups
        Analogous traits rise NOT through common ancestry, but through independent adaptation to similar environments
        Similar structure and function, but different ancestors
        Ex. sugar glider and flying squirrel
- - - - Gene variation originates when mutation, gene duplication, or other processes produce new alleles and new genes.
        
        Gene variations are produced rapidly in organisms with short generation times
        
        Sexual reproduction can produce genetic variation by recombining existing alleles.
      - Formation of New Alleles
        
        New alleles arise by mutation- change in nucleotide sequence of DNA.
        Mutations can be caused by replication errors or exposure to certain types of radiation or chemicals.
        
        Even point mutations (change in single nucleotide) can have significant impact on phenotype.
        
        Organisms reflect many generations of past selection, so phenotypes tend to be well suited for their environments.
        
        In some cases, natural selection quickly removes harmful alleles. In diploid organisms, harmful alleles can be masked by heterozygous individuals- heterozygous protection
        -Maintains a pool of alleles that could be beneficial if environment changes.
        
        Not all mutations are harmful.
        Neutral variation- variation with no selective advantage in the genetic code.
        -Usually caused by point mutations in noncoding regions.
        -Occurs within genes due to the redundancy in the genetic code.
        
        In multicellular organisms, only mutations in cell lines that produce gamete can be passed to offspring.
      - Altering Gene Number or Position
        
        Large chromosomal mutations that delete, disrupt, or rearrange any loci tend to be harmful.
        
        Duplication of small segments of DNA is a key potential source of genetic variation.
        If duplicated genes persist over generations, mutations accumulate and new functions may arise.
        
        Increase in gene number likely played a major role in evolution.
        Ex. ancestral mammalian gene for odor detection has been duplication many times- leading to many functional olfactory receptor genes.
      - Rapid Reproduction
        
        Although mutation rates are low, organisms like prokaryotes have shorter generation times that allow mutations to accumulate rapidly.
        Ex. Mutations in viruses can accumulate rapidly due to short generation ties and rapid mutation rates.
      - Sexual Reproduction
        
        Genetic variation in sexual reproduction results from recombination of alleles.
        
        Recombination occurs through three mechanisms:
        Crossing over-exchange of genetic info. between homologous chromosomes during meiosis.
        Independent assortment-random distribution of chromosomes into gametes during meiosis.
        Fertilization-random combination of gametes.
- - - - If a population is not evolving, genotype and allele frequencies will be constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work.- Hardy-Weinberg equilibrium
        calculate the allele frequency, then use the rule of multiplication to calculate the frequencies of the three possible genotypes.
      - If p and q represent the relative frequencies of the only two possible alleles in a population at a particular locus:
        p² + 2pq + q²=1
        
        p² and q² represent the frequencies of the homozygous genotypes, and 2pq represents the frequency of the heterozygous genotype.
        
        Probability that two Cr alleles come together= p x p=p²= 0.8 x 0.8²=0.64 (64%)
        64% of next generation of plants will have genotype CrCr.
        CwCw= q x q = q²= 0.2 x 0.2= 0.04 (4%)
        CrCw= p x q= 0.2 x 0.8= 0.16 (16%)
        sum of these possibilities= pq + pq= 2pq= 0.16 + 0.16= 0.32 (32%)
        MUST ADD TO 100%
        64% + 4% + 32%= 100%
      - Conditions for Hardy-Weinberg Equilibrium
        
        In real populations, allele and genotype frequencies often do change over time.
        
        A deviation from any of these conditions is a potential cause of evolution.
        
        Required Conditions for Hardy-Weinberg Equilibrium
        1. No mutations- gene pool is modified if mutations occur or if entire genes are deleted/duplicated.
        2. Random mating-mating with a subset of the population (close relatives), random mixing of gametes does not occur and genotype frequencies change.
        3. No natural selection- allele frequencies change when individuals with differing genotypes show consistent differences in survival or reproductive success.
        4. Extremely large population size- in small populations, allele frequencies fluctuate by chance over time (genetic drift)
        5. No gene flow- By moving alleles into or out of populations, gene flow can alter allele frequencies.
        
        Some genes can be in equilibrium while others are not- if selection alters frequencies at specific loci.
        
        Some populations evolve so slowly that change in allele and genotype frequencies is indistinguishable from that expected for a non-evolving population.
    - - Used to test whether evolution is occurring in a population.
        
        Used to determine the percentage of a population carrying a specific allele.
        Ex. PKU phenylketonuria is Hardy-Weinberg equilibrium given:
        
        PKU gene mutation rate is low.
        
        Mate selection is random with respect to whether or not an individual is a carrier for the PKU allele.
        
        Natural selection can only act on rare homozygous individuals who do not follow dietary restrictions.
        
        Population is large; genetic drift is not a factor.
        
        Migration has no effect, many other populations have similar allele frequencies.
      - Occurence of PKU is one per 10,000 births
        q²= 0.0001
        q= √0.0001=0.01
        
        Frequency of dominant allele
        p=1-q=1=0.01=0.99
        
        Frequency of carriers
        2pq=2x0.99x0.01=0.0198
        ~approximately 2% of the US population.
- - - - Founder Effect
        
        Founder effect- when a few individuals become isolated from a larger population.
        Ex. Few members of a population are indiscriminately blown by a storm to a new island.
        
        Smaller group may establish a new population whose gene pool differs from the source population.
        
        Accounts for relatively high frequency of certain inherited disorders among isolated human populations.
      - Bottleneck Effect
        
        Bottleneck effect- occurs when there is a drastic reduction in population size due to a sudden change in the environment.
        Ex. Fire or flood or manmade
        
        The resulting gene pool may not reflect the original population's gene pool
        
        Case Study: Impact of Genetic Drift on the Greater Prairie Chicken
        
        Loss of the prairie habitat from farming caused severe reduction in population of greater prairie chickens in Illinois.
        
        Surviving birds had little genetic variation and only 50% of eggs were hatching.
        
        Researchers compared DNA between museum specimens and the current population- genetic variation had declined and harmful alleles had increased.
        
        Researchers added 271 birds from neighboring states' populations- new alleles entered the population and egg hatching rate improved over 90%.
- - - - Directional selection- conditions favor individuals exhibiting one extreme of a phenotypic range.
        
        Shifts population's frequency curve for the phenotypic character in one direction or the other.
        
        Common when environment changes of members migrate to a different habitat.
      - Disruptive selection- favors individuals at both extremes of the phenotypic range over intermediate phenotypes.
        Ex. Small-billed finches feed on soft seeds, whereas large-billed birds crack hard seeds. Intermediate-billed birds are inefficient at cracking both types of seeds and have a lower relative fitness.
      - Stabilizing selection- favors intermediate variants and acts against extreme phenotypes.
        
        Reduces variation and tends to maintain the status quo for particular phenotypic character.
        Ex. birth weight range
  - - - Frequency-dependent selection- fitness of a phenotype depends on how common it is.
        Ex. scale-eating fish
    - - Heterozygote advantage- occurs when heterozygotes have a higher fitness than both kinds of homozygotes.
        
        Natural selection will maintain two or more alleles at that locus.
        Ex. An individual heterozygous for sickle cell maintains high frequency due to its advantage against malaria and lack of sickle cell symptoms.
        
        Heterozygotes have an advantage over homozygotes.