分子生物学（双语）7 Clusters and Repeats.ppt

Chapter 7 Clusters and Repeats FIGURE CO: Clusters and Repeats ? MedicalRF.com/Visuals Unlimited FIGURE 01: Chiasma formation represents the generation of recombinants FIGURE 02: Recombination involves pairing between complementary strands of the two parental duplex DNAs FIGURE 03: Unequal crossing-over results from pairing between nonequivalent repeats in regions of DNA consisting of repeating units FIGURE 04: Gene number can be changed by unequal crossing-over FIGURE 05: a thalassemias result from various deletions in the a-globin gene cluster FIGURE 06: Deletions in the b-globin gene cluster cause several types of thalassemia FIGURE 07: A tandem gene cluster has an alternation of transcription unit and nontranscribed spacer and generates a circular restriction map FIGURE 08: The nucleolar core identifies rDNA under transcription, and the surrounding granular cortex consists of assembling ribosomal subunits Photo courtesy of Oscar Miller. FIGURE 09: Transcription of rDNA clusters generates a series of matrices, each corresponding to one transcription unit and separated from the next by the nontranscribed spacer Photo courtesy of Oscar Miller. FIGURE 10: The nontranscribed spacer of X. laevis rDNA has an internally repetitious structure that is responsible for its variation in length FIGURE 11: Unequal recombination allows one particular repeating unit to occupy the entire cluster FIGURE 12: Mouse DNA is separated into a main band and a satellite by centrifugation through a density gradient of CsCl FIGURE 13: Cytological hybridization shows that mouse satellite DNA is located at the centromeres Photo courtesy of Mary Lou Pardue and Joseph G. Gall, Carnegie Institution. FIGURE 14: Satellite DNAs of D. virilis are related FIGURE 15: The repeating unit of mouse satellite DNA contains two half-repeats, which are aligned to show the identities (in blue)