Dr. Morris Maduro, UC Riverside Biology 168 – 10F – Lecture 4, page 1Lecture #4: Drosophila: Overall development, embryonic polarity, maternal/zygotic genes, Textbook: 2nd Ed.: 48-51. 3rd Ed.:31-34. Some figures in these notes are redrawn or reproduced from Wolpert et al. (2nd or 3rd editiosn). Importance of DrosophilaThe fruit fly is one of the most understood animals in terms of development and genetics. People have been working on Drosophila melanogastersince Thomas Hunt Morgan’s time in the early part of the last century. Flies are small, are easy to manipulate in the laboratory, and grow relatively quickly. As we will find out, the genes that pattern the Drosophilaembryo are evolutionarily conserved. In 1995 the Nobel prize was awarded to Ed Lewis, Christiane Nüsslein-Volhard, and Eric Weishaus, the scientists that used genetics to describe how the embryo is patterned. Overview of Drosophiladevelopment This is overall life cycle of the fruit fly at 25ºC. It takes nine days to make a fly, which becomes sexually mature within two days. The female produces an egg, abo5mm (¼ inch) long, which gets fertilized by male sperm through the micropyleat the anterior end of the egg. The haploidmale anfemale nuclei fuse to form the diploid zygote nucleus. The nuclei undergo a series of rapid cdivisions until there are thousands of nuclei along the outside surfawhich constitutes the synblastodermstage. ut d ell ce, cytial After three hours, gastrulationstarts, which is the inward movement of the future mesoderm and endoderm. The embryo hatches out as a feeding larva, which will grow and progress through two molts, or instars, before forming a pupa. The pupa metamorphosesinto the adult. During this process most of the larval tissue is lost. The larvae contain tiny structures called imaginal discswhich are the progenitors of adult structures such as the wings, legs and eyes. The Early EmbryoAfter fertilization, the zygote nucleusundergoes a series of very rapid divisions (mitosis) in the absenceof cell division (i.e. no cytokinesis). As such, you have many nuclei sharing the same cytoplasm (a syncytium). The nucleus undergoes 8 divisions to produce 256 nuclei (~8 min/division). The nuclei migrate to the periphery of the egg and continue to divide (at a slower rate). At division cycle 9, a small number of nuclei at the very posterior become pole cells, the progenitors of the germ line. At cycle 10,
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