Some researchers claim that sponge genomes have

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73) Some researchers claim that sponge genomes have homeotic genes, but no Hox genes. If true, this finding would A) strengthen sponges' evolutionary ties to the eumetazoa. B) mean that sponges must no longer be classified as animals. C) confirm the identity of sponges as "basal animals." D) mean that extinct sponges must have been the last common ancestor of animals and fungi. E) require sponges to be reclassified as choanoflagellates. Answer: C Topic: Concept 32.4 Skill: Application/Analysis Table 32.1. Proposed Number of Hox Genes in Various Extant and Extinct Animals Last Common Ancestor of Bilateria Last Common Ancestor of Insects and Vertebrates Ancestral Vertebrates Mammals 4 7 14 38-4 22
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74) What conclusion is apparent from the data in Table 32.1? 75) All things being equal, which of these is the most parsimonious explanation for the change in number of Hox genes from the last common ancestor of insects and vertebrates to ancestral vertebrates, as shown in Table 32.1? A) The occurrence of 7 independent duplications of individual Hox genes. B) The occurrence of 2 distinct duplications of the entire 7-gene cluster, followed by the loss of one cluster. C) The occurrence of a single duplication of the entire 7-gene cluster. Answer: C Topic: Concept 32.4 Skill: Application/Analysis 76) Two competing hypotheses to account for the increase in the number of Hox genes from the last common ancestor all bilaterians to the last common ancestor of insects and vertebrates are: (1) a single duplication of the entire 4-gene cluster, followed by the loss of one gene, and (2) 3 independent duplications of individual Hox genes. To prefer the first hypothesis on the basis of parsimony requires the assumption that Self-Quiz Questions 1) Among the characteristics unique to animals is A) gastrulation. B) multicellularity. C) sexual reproduction. D) flagellated sperm. E) heterotrophic nutrition.
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