Introduction to Genetic Analysis 594

Introduction to - 44200_18_p575-610 1:34 PM Page 593 18.5 Forming complex pattern utilizing positional information to establish cell fates 593

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Unformatted text preview: 44200_18_p575-610 3/17/04 1:34 PM Page 593 18.5 Forming complex pattern: utilizing positional information to establish cell fates 593 Figure 18-21 Scanning electron micrographs of (a) a 3-hour Drosophila embryo, (b) a 10-hour embryo, and (c) a newly hatched larva. Note that outlines of individual cells are visible by 3 hours; by 10 hours, the segmentation of the embryo is obvious. Lines are drawn to indicate that the segmental identity of cells along the A – P axis is already fated early in development. The abbreviations refer to different segments of the head (CL, PC, O, D, Mx, Ma, Lb), thorax (T1 to T3), and abdomen (A1 to A8). [T. C. Kaufman and F. R. Turner, Indiana University.] (a) 3-hour embryo (b) 10-hour embryo The A – P cardinal genes are also known as gap genes, because flies that have mutations in these genes do not have the proper sequential set of larval segments: there is a gap in the normal segmentation pattern. (For examples, look at the phenotypes of mutations in two gap genes, Krüppel and knirps in Figure 18-22). Through Figure 18-22 Types of Drosophila mutants. These diagrams depict representative mutants in each class of mutant larval phenotypes due to mutations in the three classes of zygotically acting genes controlling segment number in Drosophila. The red trapezoids are segmentally repeating swatches of dense projections on the ventral surface of the larval exoskeleton. The boundary of each segment is indicated by a dotted line. The left-hand diagram of each pair depicts a wild-type larva, and the right-hand diagram shows the indicated A – P mutant. The pink regions on the wild-type diagram indicate the A – P domains of the larva that are missing in the mutant. Pair Rule Segment Polarity (c) Newly hatched larva Gap Krüppel even-skipped odd-skipped gooseberry knirps paired runt patched ...
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

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