Evolution Problem Drill 09: The Tree of Life

Transcription

1 Evolution Problem Drill 09: The Tree of Life Question No. 1 of 10 Question 1. The age of the Earth is estimated to be about 4.0 to 4.5 billion years old. All of the following methods may be used to estimate the age of the Earth except which? Question #01 (A) Radiometric dating the amount of a particular radioisotope may be measured in ancient rocks to determine when the rocks originated. (B) Measuring the amount of carbon dioxide present in ice core samples. (C) Radiometric dating The amount of a particular radioisotope may be measured in rocks from the Earth s moon. (D) Measuring the age of meteorites because they should have been created at about the same time as the Earth. Radiometric dating using ancient rocks from the Earth is one way to determine the age of the Earth. B. Correct! Measuring the amount of carbon dioxide in ice core samples will not tell you anything about the age of the Earth. Radiometric dating using rocks from the Earth s moon is one way to determine the age of the Earth. Measuring the age of meteorites, using radiometric dating, is one way to determine the age of the Earth. Note that this question is asking which of the methods describe about measuring the age of the Earth is NOT used. Therefore, the correct answer is the answer that suggests that measuring the amount of carbon dioxide from ice cores is useful in determining the age of the Earth. The best way to measure the age of the Earth is through radiometric dating. Radiometric dating is useful because we can measure the amount of a particular radioisotope in ancient rocks of the Earth and estimate their age. This is possible because after rocks are created, these isotopes decay at a steady rate, allowing us to estimate when the rocks were created based on how much of the isotope is currently present. However, we have been able to get more accurate estimates using rocks from meteorites and from the moon, which should have been created at about the same time as the Earth. This is true because the crust of the Earth is constantly being recycled and determining which rocks are ancient is difficult.

2 Question No. 2 of 10 Question 2. All of the following is evidence that the Earth has change since its origin except which of the following? When constructing the tree of life, what type of data/characters should you use? Question #02 (A) Fossils of the same species from long ago can be found in both South America and Africa despite the distance between these continents today. (B) Ice core samples that suggest that carbon dioxide levels fluctuate over time, resulting in periodic ice ages. (C) Tree rings that suggest cyclic patterns in rainfall over the past 100 years. (D) Carbon dating of human like fossils. This evidence suggests that South America and Africa existed in closer proximity sometime in the past compared to today plate tectonics. This evidence suggests that the Earth s climate has changed over time. This evidence suggests that the Earth s climate is changing even today. D. Correct! This evidence does not suggest that the Earth is changing over time, but that life on Earth is changing. Note that this question is asking for which of the following statements does NOT provide evidence that the Earth has changed over time. The Earth has physically changed over time through the movement of the continents and through changes in the atmosphere and climate. There is evidence that the Earth s land masses are moving even today. Fossil patterns suggest that the Earth once had one huge land mass, and that this land mass has separated and slowing moving to form the continents that we observe today. The fact that we can find similar fossils on continents that are separated today by oceans suggests that these land masses once existed much closer to each other. In addition, we know that the Earth s atmosphere and climate have changed over time. We have evidence from ice core samples, from which we can obtain carbon dioxide levels from the past and also from sediment samples and even tree rings. It is well known that carbon levels fluctuate over time and that temperature is in turn affected. Low carbon levels are associated with ice ages from the past.

3 Question No. 3 of 10 Question 3. Why was the discovery of ribozymes important to the Abiotic Origin of life on Earth theory? Question #03 (A) Ribozymes are RNA molecules with only the ability to replicate. (B) Ribozymes are RNA with catalytic activity, giving them the potential to replicate and evolve. (C) Ribozymes are DNA with protein like activity, giving them the potential to replicate and evolve. (D) Ribozymes are DNA molecules with only the ability to replicate. Ribozymes are RNA molecules, but they also have the ability to evolve. B. Correct! Ribozymes are RNA molecules that possess catalytic activity, giving them both a genotype and phenotype. Ribozymes are not DNA molecules. Ribozymes are not DNA molecules. Ribozymes are important to the Abiotic Origin of life on Earth theory because they are simple molecules that have the capacity to both replicate and evolve. A ribozyme is an RNA molecule with catalytic activity. Therefore, this molecule has both a genotype (RNA is a heritable material) and a phenotype (protein-like catalytic activity), and perhaps the potential to self-replicate. Because ribozymes have been experimentally shown to evolve, it is thought that proteins and nucleic acids may have formed the first cells, and thus the first life on Earth.

4 Question No. 4 of 10 Pick the answer (4) Go back to review the core concept tutorial as needed. Question 4. How does horizontal gene transfer affect the Tree of Life? Question #04 (A) Horizontal gene transfer does not affect the tree of life because the tree of life is based on relatedness due to common descent. (B) Horizontal gene transfer affects the tree of life because genes can be transferred between individuals within the same generation and between generations. (C) Horizontal gene transfer affects the tree of life because with horizontal gene transfer, genes are transferred from one generation to the next. (D) Horizontal gene transfer affects the tree of life because genes are no longer transferred from parent to offspring. If the tree of life is based on relatedness due to common descent, or vertical gene transfer, then horizontal gene transfer should affect species relationships and affect the tree. B. Correct! Genes are not only thought to be transferred vertically, but also horizontally. Genes are not transferred from one generation to the next with horizontal gene transfer. That type of gene transfer is vertical. Genes are also transferred vertically from parent to offspring. Genes were once thought to only be transferred from parent to offspring, from one generation to the next, in a vertical fashion. The tree of life was consequently supposedly based on this vertical transmission of genes and should represent relationships between species based on relatedness to common ancestors. With the occurrence of horizontal gene transfer, genes are being exchanged between species that exist at the same time (horizontal) and between ancestral species and their descendents (vertical). Therefore, many genes that are used to construct the tree of life will produce different trees. Species may share genes, but not be closely related due to common descent. This creates a dilemma for tree construction and interpretation.

5 Question No. 5 of 10 Question 5. Fossil data suggest that the Cambrian explosion occurred roughly 500 to 550 million years ago. In contrast, dates based on sequence data suggest that the Cambrian explosion occurred between 900 and 1200 million years ago. Why would one expect these two approaches to yield slightly different answers? Question #05 (A) The estimate made from the sequence data is likely an over-estimate because sequence divergence would be large for a time-scale this long. (B) Estimates made from sequence data are inaccurate due to the inaccuracy of the molecular clock. (C) Estimates made from fossil data are inaccurate due to the inaccuracy of radiometric dating. (D) The estimate made from fossil data is likely an underestimate because one would not expect to observe fossils of a species until that species becomes common. Sequence divergence would be large between species that have been separated for long periods of time, but this is not why sequence data should differ from fossil data. The molecular clock has been shown to be quite accurate and useful in dating species origins and divergence times. Radiometric dating has been shown to be quite accurate as isotopes are known to decay at a predictable rate. D. Correct! Both methods are most likely accurate estimates, but the fossils did not occur until long after the actual speciation event. Fossil data and sequence data should yield different estimates of speciation events, radiations, and extinctions. This is because fossils can only be found once the species has become common enough to leave fossil evidence. It is likely that a species does not become common for a long time after a speciation event. Consequently, fossil dating necessarily underestimates the true time of a species origination. In contrast, molecular data provide an estimate of the true divergence date between two species.

6 Question No. 6 of 10 Question 6. Which of the following statements is not correct about biological classification? Question #06 (A) All of the butterflies within the Nymphalidaea Family are also part of the same Class. (B) All of the plants within Liliopsida Class are also part of the same Phylum. (C) Biological classification was originally based on relationships between organisms based on common ancestry. (D) Biological classification was originally based on relationships between organisms based on similarities. This statement is correct. All organisms within a Family are also part of all categories of classification above Family. This statement is correct. All organisms within a Class are also part of all categories of classification above Class. C. Correct! Biological classification was not originally based on common ancestry. Biological classification was originally based on similarities between organisms, and still is. Note that this question is asking for which of the following statements is NOT correct about biological classification. Biological classification has occurred since the time of the early Greek philosophers and was originally based on similarities between organisms. If two organisms looked alike it was assumed that they belonged within the same category or were closely related. Classification today is also based on similarities between organisms, but we have more traits to observe and compare with the advent of molecular biology and genetics. We also try to classify organisms now based on common ancestry, which can often be elicited using molecular data and techniques. Because of this biological classification often reflects evolutionary history, which is based on relatedness due to common ancestry. The important thing to remember with biological classification is that similar organisms are grouped as species and species grouped into Genus, etc. organisms are placed into bigger and bigger collections so that all organisms that fit into the category before also all belong to the higher category. The largest category is Kingdom and the smallest, species.

7 Question No. 7 of 10 Question 7. Which of the following statements is correct about the 5 identified mass extinctions? Question #07 (A) The Triassic mass extinction occurred about 200 mya and included the extinction of the dinosaurs. (B) The Cretaceous mass extinction is thought to have been caused by a large body mass that hit near the Yucatan Peninsula in Mexico. (C) The largest mass extinction included the loss of 50% of the marine life. (D) The oldest mass extinction may have been caused by global warming. The Triassic mass extinction did not include the extinction of the dinosaurs. B. Correct! It is thought that an asteroid caused the Cretaceous mass extinction 65 mya. The largest mass extinction included the loss of 95% of the marine life. The oldest mass extinction was likely caused by a glaciation event. The following information characterizes each of the 5 mass extinction events: Ordovician (440 mya) loss of about 50% of animals; may have been caused by glaciation event. Devonian (365 mya) lasted about 3 my and characterized by several short extinction events and loss of many warm water species; may have been caused by climate change/global cooling. Permian (215 mya) largest mass extinction with 95% loss of marine life and 70% loss of land organisms; may have been caused by land mass movement. Triassic (200 mya) least significant mass extinction; may have been caused by climate change. Cretaceous (K-T) (65 mya) second largest mass extinction characterized by loss of dinosaurs; may have been caused by asteroid that hit near Yucatan Peninsula.

8 Question No. 8 of 10 Question 8. From the explanations below, choose the best answer that explains the probable fate of any given species? Question #08 (A) The fate of any given species is that it will exist into perpetuity. (B) The fate of any given species is that it will speciate and form two new species. (C) The fate of any given species is that it will go extinct. (D) The fate of any given species is that it will remain unchanged with time. Most species have gone extinct. Although this is possible, it is not the most likely fate of any given species. C. Correct! Out of all species that ever existed, nearly all are extinct. A species is likely to undergo genetic changes with time due to changing environments and chance. The probably fate of any given species from the past or present is that it will go extinct. Out of all species that ever existed, most are extinct. The number of extant species that exist today is miniscule in comparison to the number that existed in the past and eventually went extinct. Extinction is nearly certain. However, note that there is a balance between extinction and speciation for any given time. That is, overall biodiversity remains relatively constant except in the instance of a mass extinction event. However, given enough time after a mass extinction event, the balance will return.

9 Question No. 9 of 10 Question 9. Endosymbiosis of organelles is a special example of a horizontal transfer even between species. Which of the following statements about endosymbiosis below is not correct? Question #09 (A) Endosymbiotic events likely only occurred once, but were followed by secondary events that established there role. (B) The chloroplasts of plants are thought to have evolved through endosymbiosis between a eukaryote and cyanobacterium. (C) The mitochondria of eukaryotes are thought to have evolved through the endosymbiosis between a eukaryote and proteobacteria. (D) Endosymbiotic events should not have any affect on the relationships that exist between the three domains. This statement is true. Endosymbiotic events likely only occurred once. This statement is true. Chloroplasts and cyanobacteria are very similar. This statement is true. Mitochondria and proteobacteria are very similar. D. Correct! This statement is not true. Endosymbiotic events result in similar genomic material between very different species. Note that this question is asking for which statement about endosymbiosis is NOT correct. Endosymbiosis is a horizontal transfer event that results in a symbiotic relationship between two organisms. Endosymbiosis is thought to be responsible for the acquisition of photosynthetic capabilities in plants and the mitochondria of eukaryotes. It is thought that these eukaryote cells engulfed bacterial cells and incorporated their genomes into there own, resulting in chloroplasts and mitochondria. Evidence that this occurred is that the genetic make-up of chloroplasts and mitochondria in eukaryotes is very similar to the genetic make-up of cyanobacteria and proteobacteria, respectively. These events likely only occurred once, but were then followed by secondary events that established there existence. Because of horizontal transfer events like this, eukaryotes and bacteria may appear to be more closely related then they truly are because of the similar genetic make-up. In fact, eukaryotes are more closely related to archaea than bacteria.

10 Question No. 10 of 10 Question 10. Which theory would Darwin have preferred, punctuated equilibrium or phyletic gradualism, and why? Question #10 (A) Darwin would have likely preferred the theory of phyletic gradualism because he did not have a fossil record to suggest that evolution occurs in any other way but slowly over time. (B) Darwin would have likely preferred the theory of phyletic gradualism because he observed abrupt changes in finch species during the time he spent on the Galapagos Islands. (C) Darwin would have likely preferred the theory of punctuated equilibrium because he was able to observe abrupt evolutionary changes within and between species in his lifetime. (D) Darwin would have likely preferred the theory of punctuated equilibrium because there was an extensive fossil record for him to study to suggest this pattern of evolution. A. Correct! Darwin believed that evolution was a slow and gradual process and did not have evidence otherwise. Phyletic gradualism would not be consistent with abrupt changes in finch species over a short amount of time. Darwin did not observe abrupt evolutionary changes within his lifetime. Darwin did not have the luxury of an extensive fossil record to study. Charles Darwin most likely would have supported the theory of Phyletic Gradualism over Punctuated Equilibrium given the evidence and observations he made during his lifetime. He believed evolution was a slow and gradual process and that species changed slowly over time, eventually leading to speciation. This is evident from his drawing of a phylogenetic tree in the Origin of Species. Punctuated Equilibrium is the idea that changes in life on Earth occur during speciation events through large-scale abrupt changes. There is evidence for this type of change in the fossil record, where we observe very little change for large periods of time followed by large changes over short periods of time. This theory suggests that evolution occurs all at one time and that in between these times there are evolutionary static periods. Observations like these in the fossil record may be due to how species speciate. It is possible that these large, abrupt changes occur in small populations where the effects of drift are much more pronounced compared to larger populations of the same species. The larger populations will remain relatively static in comparison because genetic changes are occurring more slowly. However, fossils may not accumulate for these small populations simply by chance and abruptly appear in the fossil record once the larger populations have caught up, making it appear like speciation and evolution is punctuated. Phyletic Gradualism on the other hand is the idea that changes in life on Earth occur steadily and gradually over time. That is, genetic changes are slow and gradual within species over time and during speciation events. If Gradualism is true, the fossil record should reflect constant change over time. The lack of this evidence in the fossil record may be due to missing fossil data. Perhaps the intermediate forms just have not been discovered yet.

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