please answer all of the questions answering only one question is not helpful 16
ID: 273333 • Letter: P
Question
please answer all of the questions answering only one question is not helpful
16. Directional selection is one of the models of natural selection. Describe this type of selection in terms of the frequencies of advantageous alleles over time. What is the trend over time? What is the eventual outcome for this allele as long as no other evolutionary factors intervene? Describe at least one good example of directional selection. ?
17. Consider the first copy of an allele for insecticide resistance that arises by mutation in a population of insects exposed to an insecticide. Is this mutation an adaptation? If, after some generations, we find that most of the population is resistant, is the resistance an adaptation? If we discover genetic variation for insecticide resistance in a population that has had no experience of insecticides, is that variation an adaptation? If an insect population is polymorphic for two alleles, each of which confers resistance against one of two pesticides that are alternately applied, is that variation an adaptation? Or is each of the two resistance traits an adaptation? Explain your reasoning thoroughly. ?
18. Fossils provide valuable information on evolutionary trends and ancestral character states. Unfortunately by their very nature, the fossil record can never be complete. Explain why the fossil record will never be complete. Explain how fossils are formed and the various types of fossils. An ideal fossil record would enable researchers to distinguish the patterns of phyletic gradualism, punctuated equilibria, and punctuated gradualism (Figure 4.18). How would you do so? How do imperfections of the fossil record make it difficult to distinguish these patterns? ?
19. Polymorphisms for a given trait are relatively common in most species. Discuss the possible advantages or polymorphisms in terms of evolutionary fitness. Be sure to relate your discussion to a specific example. It is also possible that organisms showing more heterozygosity may actually be less fit. Describe one such possible scenario. ?
20. In the peppered moth (Biston betularia), black individuals may be either homozygous (A1A1) or heterozygous (A1A2), whereas the pale gray moths are homozygous (A2A2). Suppose that in a sample of 250 moths from one locality, 108 are black, and 142 are gray. ?
a.Which allele is dominant? ?
b.Assuming that the locus is in Hardy-Weinberg equilibrium, what are the allelic frequencies? ?
c. Under this assumption, what proportion of the sample is heterozygous? What is the number of ?heterozygotes? ?
d.Under the same assumption, what proportion of black moths is heterozygous? ?
e.Why is it necessary to assume Hardy-Weinberg genotypic frequencies in order to answer a-d? ?
21. Suppose that a mutation in a species of annual plant increases allocation to chemical defenses against herbivores, but decreases production of flowers and seeds (i.e., there is an allocation trade-off). What would you have to measure in a field study in order to predict whether or not the frequency of the mutation will increase? ?
22. The popular media often presents evolution as being a predictable process with a definite goal. For instance, in one “Star Trek: Voyager” episode, the captain instructs the ship’s computer to extrapolate the “probable course” of evolution of hadrosaurs (a bipedal dinosaur), if hadrosaurs had been removed from Earth before the Cretaceous-Tertiary (K-T) Extinction and allowed to evolve on another planet. What information about the hadrosaurs’ new environment would have been useful in developing the best possible prediction? Given what you know on genetic drift and selective agents, is it possible to accurately predict the long-term course of evolution? ?
23. Paleontologists and some biologists commonly infer function, and even behavior, from anatomical details. Skeletal features, for example, are often used to infer that an extinct mammal (such as an early hominin) was highly, somewhat, or not at all arboreal. This inference assumes a good fit of form to function (i.e., optimal form). Can this assumption be justified? ?
24. Consider a species of sparrow that originally lived only in Alaska but recently expanded its range through North America, then Central America, and finally South America. How would you expect heterozygosity for most loci to differ among populations in North America, Central America, and South America? Why? Which of those regions would you expect to have the most genetically similar populations, and the most different? ?
25. Consider a cricket that has recently colonized a remote ocean island from a source population on a continent. How do expect the average size of the wings in the island population to compare with the average size on the continent? How do you expect wing size in the island population to evolve over the next several hundred generations? ?
26. The concept of a species is fundamental to understanding biology, yet there may not be one definition that fits all “types” of organisms (e.g. animals, plants, fungi, bacteria, slime mold, lichens, etc.). Discuss several of the definitions of a species as presented in class and present your own definition for a species. Compare the strengths and weaknesses of each definition. Ernst Mayr is strong proponent of the biological species concept. How does he justify his position? Do you agree or disagree? If we employ the biological species concept, when did species first exist? What were organisms before then, if not species? What might the consequences of the emergence of species be for processes of adaptation and diversification? Be sure to explain your reasoning thoroughly. ?
27. The process of speciation ultimately involves the development of reproductive isolation between two related populations of organisms. Describe the various types of both prezygotic and postzygotic reproductive isolation and give an example of each. ?
29. Stephen Jay Gould (1989) and others have argued that the evolution of self-conscious, intelligent species (i.e. humans) was historically contingent: it would not have occurred had any of a great many historical events been different. The philosopher Daniel Dennett (1995) and others have disagreed, arguing that convergent evolution is so common that if humans had not evolved, some other lineage would probably have given rise to a species with similar mental abilities. What do you think, and why? If Gould’s position is right, what are its philosophical implications, if any? ?
30. Since 2001, the complete DNA sequences of the genomes of many people have been determined. If humans, along with other forms of life, have evolved from a common ancestor, what evidence of this would be expected in the human genome? In what ways might the history and processes of evolution help us interpret and make sense of the human genome sequence data?
Explanation / Answer
Q27) The view of species as entities subjected to natural selection and amenable to change put forth by Charles Darwin and Alfred Wallace laid the conceptual foundation for understanding speciation. Initially marred by a rudimental understanding of hereditary principles, evolutionists gained appreciation of the mechanistic underpinnings of speciation following the merger of Mendelian genetic principles with Darwinian evolution. Only recently have we entered an era where deciphering the molecular basis of speciation is within reach. Much focus has been devoted to the genetic basis of intrinsic postzygotic isolation in model organisms and several hybrid incompatibility genes have been successfully identified. However, concomitant with the recent technological advancements in genome analysis and a newfound interest in the role of ecology in the differentiation process, speciation genetic research is becoming increasingly open to non-model organisms. This development will expand speciation research beyond the traditional boundaries and unveil the genetic basis of speciation from manifold perspectives and at various stages of the splitting process. This review aims at providing an extensive overview of speciation genetics. Starting from key historical developments and core concepts of speciation genetics, we focus much of our attention on evolving approaches and introduce promising methodological approaches for future research venues.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.