AP Biology Unit 1 Study Guide

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Explain why bird and bat wings are homologous as vertebrate forelimbs but analogous as wings.
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Bird and bat wings originated from a common tetrapod ancestor, therefore they are homologous as vertebrate forelimbs. However, the wings themselves are analogous because they arose independently from the forelimbs of different tetrapod ancestors.
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Explain why the occurrence of horizontal gene transfer has led to the suggestion that the history of life should be represented by a ring rather than a tree.
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Through horizontal gene transfer, DNA is being transferred from one prokaryotic organism to another. This increases genetic diversity faster because DNA transfers within a generation rather than having to wait from one generation to the next. This evolutionary relationship can only be depicted by a ring, not a tree.
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Describe the evidence that suggests that RNA was the first genetic material. Explain the significance of the discovery of ribozymes.
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RNA was most likely the first genetic materials because they are capable of replicating faster and is less protected, thus they do not correct errors very well. It is also much shorter than DNA and is single stranded rather than double stranded. There are multiple versatile types of RNA: mRNA, rRNA, and tRNA. Early protobionts containing enzymatic RNA could use their resources effectively, and thus increase through natural selection. The discovery of ribozymes led to this theory.
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Why is it likely that Hox genes have played a major role in evolution of novel morphological forms?
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In animal embryos, Hox genes influence the development of structures such as limbs and feeding appendages. As a result, changes in these genes can lead to major effects on morphology.
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Of all the mutations that occur in a population, why do only a small fraction become widespread among the population’s members?
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Many mutations occur in somatic cells that do not produce gametes, therefore the mutations are lost when the organism dies. Of the mutations that occur in gamete producing cells, they usually are not inherited because they do not increase the organism’s reproductive success.
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List 4 reasons why natural selection cannot product perfect organisms.
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1. Selection can act only on existing variations 2. Evolution is limited by historical constraints 3. Adaptations are often compromises 4. Chance, natural selection, and the environment interact
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List the 5 conditions that must be met for a population to remain in Hardy-Weinberg equilibrium.
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1. No mutations 2. Random mating 3. No natural selection 4. Extremely large population size 5. No gene flow
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What is a molecular clock? What assumption underlies the use of a molecular clock?
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A molecular clock is a way to measure the absolute time of evolutionary change based on the observation that some genes and other regions of genomes appear to evolve at constant rates. The assumption underlying is that the number of nucleotides in genes is proportional to the time that has elapsed since the species branched from their common ancestor.
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What are the 5 prezygotic reproductive barriers?
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1. Habitat isolation 2. Temporal isolation 3. Behavioral isolation 4. Mechanical isolation 5. Gametic isolation
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Habitat Isolation
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-2 species that occupy different habitats may encounter each other rarely even though there are no physical barriers -Marine iguanas are isolated in their habitat from other iguanas
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Temporal Isolation
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-Species that breed during different times of the day, season, or year cannot mix their gametes -eastern and western skunk mate in spring and winter
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Behavioral Isolation
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-Courtship rituals that attract mates enable mate recognition, a way to identify potential mates of the same species -Blue footed boobies have a specific dance to attract mates of the same species
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Mechanical Isolation
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-Mating is attempted, but morphological differences prevent its successful completion -snail whorls in opposite directions make it mechanically impossible to reproduce
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Gametic Isolation
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-Sperm of one species may not be able to fertilize the eggs of another species -The gamete of one sea urchin is unable to penetrate the gamete of another so reproduction cannot occur
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Summarize key difference between allopratic and sympatric speciation. Which type is more common and why?
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In allopratic speciation, a new species forms while in geographic isolation from its parent. In sympatric speciation, a new species forms in absence of geographic isolation. It occurs due to behavioral or physiological differences. Allopatric is more common because isolation reduces gene flow.
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Why is the percentage similarity in the gene always lower than the percentage similarity in the protein for each of the species?
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The same protein may be created by multiple different base sequences, allowing for different sequences to produce identical amino acids.
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Percentage Identity
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Identity percentage shows how much two sequences have the same residues at the same positions in an alignment- a higher percentage indicates a greater level of similarities, and therefore, possible relatedness.
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Max Value
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The max score represents the overall quality of query sequence and database sequence segment alignment, predicting and taking into account the insertions and deletions that are associated with evolutionary adaptations- the higher the max score, the closer the alignment.
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Is it possible to find the same gene in two different kinds of organisms but not find the protein that is produced from that gene?
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Yes, this phenomenon is made possible by latent genes, or genes in an unexpressed state. Latent genes arise due to evolutionary pressures which make it helpful for some species not to express all of their genes. Because latent genes are inactive and therefore do not create proteins, the scenario described in the question is highly possible. Two different organisms can have the same gene, but organism 1 may have it in a latent state while the other may have the same gene as organism 1, but in an active and expressed state, therefore creating the protein associated with the shared gene.
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If you found the same gene in all organisms you test, what does this suggest about the evolution of this gene in the history of life on earth?
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This suggests that the gene has probably not evolved in the history of life on earth and probably has been present for many generations.
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Does the use of DNA sequences in the study of evolutionary relationships mean that other characteristics are unimportant in such studies?
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Using DNA sequences in the study of evolutionary relationships does not mean that other characteristics are unimportant. While DNA is a very accurate representation of evolution, investigating physical characteristics can give you additional information, such as whether the species are related homologously or analogously.
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Why did you have to pull two alleles (two straws) from the bag to represent one fish?
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Each fish has two alleles for each characteristic, therefore two straws were needed to determine the fish’s color
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Why was it necessary to include the first round without predation (#1) in each trial?
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The control round determined the percentage of each color in the population of fish without any external factors, so changes could be easily recorded and compared.
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If you continued with many more generations in Test 1 — the \”Predators Prefer Blue Fish\” —do you think the blue allele would eventually be eliminated?
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The blue fish is most likely going to be eliminated since the frequency of surviving blue fish diminished. If we continue with more generations, the blue fish would eventually have difficulty of passing on unfavorable alleles to its offsprings. Green fish however, may increase in number, therefore balancing the number of blue alleles in the gene pool.
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Directional
Directional
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Stabilizing
Stabilizing
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Disruptive
Disruptive
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What is the Hardy-Weinberg equation and what does each part mean?
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p^2+2pq+q^2=1 p+q=1 p^2:frequency of homozygous dominant individuals p: frequency of dominant allele q^2: frequency of homozygous recessive individuals q: frequency of recessive allele 2pq: frequency of heterozygous individuals
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Genetic Drift
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Genetic drift is when changes occur in the allelic frequency due to chance rather than natural selection. Genetic drift is unpredictable because the allele frequencies is by chance. As population increases, genetic drift has less influence on the overall fitness of a specific population. Additionally, as population increases, gene fixation (the loss of alleles) decreases. There is the bottleneck and founder effect.
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DNA Cladograms
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-Compare differences in DNA bases -Species with most differences are the most distantly related -Species with least differences are the most closely related -Drawback: you may not have DNA from ancient species
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Characteristic Cladograms
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-Compare similar traits and group them -Drawback: Difficult to know whether structures are analogous or homologous, not as exact as DNA
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Homologous
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Same origin
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Analogous
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Different origin
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Outgroup
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Species that share least amount of similar traits
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Fossil Cladograms
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-Sort by date -Add traits -Drawback: Fossils aren’t always in tact, time, data is spotty, not as exact as DNA
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Phylogeny
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evolutionary relationships amongst species inferred from data
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Systematics
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the study and classification of biodiversity
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Parsimony Principle
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the simplest explanation is generally correct
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Early Earth
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-about 4.6 billion years old -reducing atmosphere -UV radiation, electricity
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Primordial Soup
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-Theory of the beginning of life -abiotic synthesis of organic molecules -polymers -protobionts -self-replicating molecules -Miller and Urey
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Protobionts
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-concentrated area of organic molecules -separate internal/external environments -semipermeable -simple chemical reactions/metabolic processes -precursors of prokaryotic cells
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Endosymbiosis
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evolution of eukaryotic cells began with endosymbiotic relationships with prokaryotes
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Mitochondria
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-contain own DNA similar to DNA in bacteria -surrounded by 2 membranes, one is original and the other is from the host -same size as bacteria -derived from purple bacteria
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Chloroplasts
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-contain own DNA similar to DNA in bacteria -surrounded by 2 membranes, one is original and the other is from the host -same size as bacteria -derived from photosynthetic bacteria
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Cambrian Explosion
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diversification of animals
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Darwin’s Theory
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-Variation: multiple alleles -Overproduction: too many offspring are born -Competition: too few resources for the large amounts of offspring -Survival of the fittest: only those best adapted to find resources in the environment will survive -New alleles over long periods of time: evolution of a species took many many years/generations (gradualism)
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Evolution
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-collective chang in phenotypes/traits of organisms through time -is not purposeful -does not produce perfect organisms -studied through fossil records, biogeography, comparative embryology, molecular biology (DNA), and artificial selection
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Microevolution
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-changes noted over a short time (several generations) -Allele frequency changes due to mutation, selection, genetic drift, and gene flow -leads to macroevolution
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Macroevolution
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-changes seen over long time frames -may lead to speciation
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Pre-Zygotic Barriers
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-impede mating or hinder fertilization if mating occurs -Habitat, temporal, behavioral, mechanical, or gametic isolation
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Post-Zygotic Barriers
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-prevent hybrid zygote from developing into a viable, fertile adult -reduced hybrid viability or fertility and hybrid breakdown
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Mutation
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-change in DNA sequence -Causes variation in alleles/genes
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Natural Selection
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-traits that influence survival are selected for or against -If traits are highly beneficial for survival, those will survive and be selected for
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Sexual Reproduction
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-recombination of alleles -New combinations of alleles creates variation, new phenotypes
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Gene Flow
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-individuals coming and going into and out of a population -Brings new variation to or away from a population
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Fitness
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an organism’s ability to survive and produce offspring
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How is mutation a random process, but natural selection not?
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Mutations occur when a gene is replicated incorrectly and cause changes in the organisms’ genotype and/or phenotype. Natural selection arises from mutations but is not random. Natural selection ensures that the organisms with traits better adapted for the environment survive to reproduce more often than those with traits that hinder their survival.

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