ch21 - Chapter 21 21.1 In C. elegans, the cell lineage that...

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Chapter 21 21.1 In C. elegans , the cell lineage that unfolds during development is essentially invariant. Why is this an advantage to someone studying development? ANS: The invariant cell lineage of C. elegans affords researchers the opportunity to follow the development of tissues and organs over time; they can observe cell division, cell movement, and cell differentiation—all leading to the formation of the adult animal. FEEDBACK: 21.1 DIFFICULTY: easy 21.2. During oogenesis, what mechanisms enrich the cytoplasm of animal eggs with nutritive and determinative materials? ANS: Unequal division of the cytoplasm during the meiotic divisions; transport of substances into the oocyte from surrounding cells such as the nurse cells in Drosophila . FEEDBACK: 21.1 DIFFICULTY: easy 21.3 Predict the phenotype of a fruit fly that develops from an embryo in which the posterior pole cells had been destroyed by a laser beam. ANS: The fly will be sterile because the posterior pole cells form the germ line in adults of both sexes. FEEDBACK: 21.1 DIFFICULTY: medium 21.4. In early C. elegans development, the EMS cell divides into two cells, MS and E. MS subsequently develops into muscle cells, neurons, and some other cells while E develops into the cells of the intestine. What do you think would happen if the E cell were destroyed by a finely focused laser beam shortly after it was formed? What would happen if material extracted from the MS cell of one embryo were injected into the E cell of another embryo? ANS: Destruction of the E cell would lead to a worm without an intestine. Injection of
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material from the MS cell of one embryo into the E cell of another embryo might change the fate of the E cell, so that it subsequently gives rise to muscle cells and neurons. FEEDBACK: 21.1 DIFFICULTY: medium 21.5 Outline the main steps in the genetic analysis of development in a model organism such as Drosophila or C. elegans. ANS: Collect mutations with diagnostic phenotypes; map the mutations and test them for allelism with one another; perform epistasis tests with mutations in different genes; clone individual genes and analyze their function at the molecular level. FEEDBACK: 21.1 DIFFICULTY: easy 21.6. Why is the early Drosophila embryo a syncytium? ANS: Mitotic division is so rapid that there is not enough time for membranes to form between cells. FEEDBACK: 21.1 DIFFICULTY: easy 21.7 In Drosophila, what larval tissues produce the external organs of the adult? ANS: Imaginal discs. FEEDBACK: 21.1 DIFFICULTY: easy 21.8. In C. elegans, homozygosity for a dumpy ( dpy ) mutation causes the animal to be shorter than wild-type. If a hermaphrodite heterozygous for such a mutation were self- fertilized, what fraction of its progeny would be dumpy? ANS:
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ch21 - Chapter 21 21.1 In C. elegans, the cell lineage that...

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