have been posting the same question an not getting an answer so please answer al
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have been posting the same question an not getting an answer
so 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. ?
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
Q18) Animal or plant had to be very "lucky" to become a fossil, and even luckier to have its fossil remains discovered. Fossilization is an infrequent occurrence that is highly dependent on chance. In the past, like today, the remains of most organisms were eaten by animals, consumed by microorganisms, or weathered away. Only dead organisms that are buried in sediment quickly can escape these destructive natural processes and become fossils. After remains have been buried and preserved, they may still be destroyed by geological processes, or exposed and weathered away before people can find them. Organisms that were very rare in their environment might never have been fossilized simply because the odds of preservation favor more numerous organisms. Animals with small and delicate bones, such as small birds and amphibians, would be less likely to be preserved and discovered than larger organisms with tougher bones. Soft-bodied organisms like worms are even more poorly represented in the fossil record because they had no hard parts that could resist decay. We usually learn of their existence only if we find fossilized burrows, or trackways or impressions left by their bodies in soft sediments. Scientists studying ancient ecosystems such as this one try to collect fossils from as many types of organisms as possible, but they never expect to find fossil evidence of everything that lived there.
How are Fossils Formed?
When living matter such as plants, animals, and other organisms die, they naturally decay completely. However, sometimes when conditions are appropriate, these remains of deal living matter are preserved as fossils. Fossils are created as a result of numerous physical and chemical processes. When an animal dies, it’s buried pretty quickly beneath layers of rock and dust known as sediment. The pressure and heat as a result of buried animal and plant can cause the tissue of the dead organism including the soft body parts of fish, plant leaves, marine invertebrates, and reptiles to emit oxygen and hydrogen, leaving a residue of carbon behind. This process is known as carbonization or distillation. Carbonization gives birth to an extensive carbon impression of the dead organism in the sedimentary rock. This process is known as fossilization. Permineralization, sometimes known as petrification, is the most common technique of fossilization. After decay of an organism’s soft parts in sediment, the hardest parts, mainly the bones, remain. The remains absorb water and minerals present in the absorbed water permeate into the spaces inside the remains, eventually forming crystals. These crystals, commoly called crystallized minerals, trigger the hardening of the remains together with the outer sedimentary rock. There is another fossilization process known as replacement. Here, the minerals that constitute the bodily remains are replaced by minerals contained in ground water after the water has totally dissolved the initial hard components of the organism. Fossils can also form from cats and molds. If the organism is totally dissolved or liquefied in sedimentary rock, it might leave behind an impression of its outer surface in the rock known as external mold. If the mold is filled with other minerals, it’s called a cast. When minerals and sediments fill up the internal cavity of a fossil such as skull and shell and the remains dissolve, internal mold forms.
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