Chromatids figure

FIGURE 12.31 A model for chromosome structure, human chromosome 4. The 2-um DNA helix is wound twice around histone octamers to form 10-um uucleosomes, each of which contains 160 bp (80 per turn). These uucleosomes are then wound in solenoid fashion with six uucleosomes per turn to form a 30-nm filament. In this model, the 30-nm filament forms long DNA loops, each containing about 60,000 bp, which are attached at their base to the nuclear matrix. Eighteen of these loops are then wound radially around the circumference of a single turn to form a miniband unit of a chromosome. Approximately 10 of these minibands occur in each chromatid of human chromosome 4 at mitosis. 

Radial arrays are best exemplified by mitotic half-spindles, which have a central MTOC, the centrosome. The centrosome consists of two centrioles (which are homologous with the basal body) surrounded by dense pericentriolar material (Kalt and Schliwa, 1993). In plant cells, the MTOC of the mitotic spindle consists of dense material only without centrioles. The plus ends of microtubules of the mitotic spindle are directed toward the equator of the cell. Some are free, and others attach to kinetochores on chromatids (see Figure 4). 

The packaging of nucleoproteins within chromatids is not random, as evidenced by the characteristic patterns observed when chromosomes are stained with specific dyes such as quinacrine or Giemsa s stain (Figure 36-6). 

Figure 36-5. The two sister chromatids of human chromosome 12 (x 27,850). The location of the A+T-rich centromeric region connecting sister chromatids is indicated, as are two of the four telomeres residing at the very ends of the chromatids that are attached one to the other at the centromere. (Modified and reproduced, with permission, from DuPraw EJ DNA and Chromosomes. Holt, Rinehart, and Winston, 1970.)...

Figure 36-12. Sister chromatid exchanges between human chromosomes. These are detectabie by Giemsa staining of the chromosomes of ceiis repiicated for two cycies in the presence of bromodeoxyuridine. The arrows indicate some regions of exchange. (Courtesy of S Wolff and J Bodycote.)...

Figure 20.28 Diagrammatic representation of mitosis in a cell with a single pair of homologous chromosomes. In prophase, the chromatin condenses into chromosomes, each of which consists of a pair of chromatids that have been formed by replication during interphase, and the nuclear envelope disappears. In metaphase, each chromatid attaches to the spindle fibres (microtubules) at a centre point, the centromere. In anaphase, the two chromatids of each chromosome become detached from each other and move to opposite poles of the cell along the microtubules. In telophase, the chromatids have reached the poles. Two nuclear envelopes then form and enclose each new set of chromatids, now once again called chromosomes. The microtubules disappear and the chromosomes uncoil and re-form into the long chromatin threads. Finally the cell membrane is drawn inward by a band of microfilaments to form a complete constriction between the newly formed nuclei, and two new cells are formed. The process is called cytokinesis.

Figure 8. Cyclophosphamid-induced sister chromatid exchange in CHO cells...

Figure 6.45 Crossover at meiosis. Two homologous chromosomes are shown aligned in the top line. Each consists of two chromatids, joined together at the centromere. A and B represent genes on one chromosome, and a and b the corresponding alleles on the other chromosome. After recombination two new gene combinations are apparent. The middle and bottom lines represent other possible methods of recombination. Source From Refs. 12 and 13.

FIGURE 24-5 Eukaryotic chromosomes, (a) A pair of linked and condensed sister chromatids from a human chromosome. Eukaryotic chromosomes are in this state after replication and at metaphase during mitosis, (b) A complete set of chromosomes from a leukocyte from one of the authors. There are 46 chromosomes in every normal human somatic cell. 

Figure 26-13 Synaptonemal complexes. (A) Aligned pairs of homologous chromatids lying 0.4 pm apart in Allium cepa. Arrows indicate "recombination nodules" which may be involved in initiating formation of crossovers. Portions of meiotic chromosomes of lily are shown at successive stages (B) Pachytene. (C) Portion of diplotene nucleus. (D) A bivalent at diplo-tene. (E) Two bivalents at diakinesis. Pairs of sister chromatids are coiled with appropriate handedness. (F) Sister chromatid cores are far apart in preparation for separation. A chiasma is present between the two central strands. (B) through (F) courtesy of Stephen Stack.279,279d (G) Pair of sister chromatids coiled with opposite handedness at metaphase. These are immun-ostained with anti-topoisomerase II antibodies. From Boy de la Tour and Laemmli.280 Courtesy of U. K. Laemmli.

Figure 27-5 (A, B) Two possible models of the 30-nm chromatin fiber.55 (A) Thoma et al.85 (B) Woodcock et al.6i 87 The fully compacted structure is seen at the top of each figure. The bottom parts of the figures illustrate proposed intermediate steps in the ionic strength-induced compaction. (C) Possible organization of the DNA within a metaphase chromosome. Six nucleosomes form each turn of a solenoid in the 30-nm filament as in (A). The 30-nm filament forms 30 kb-loop domains of DNA and some of these attach at the base to the nuclear matrix that contains topoisomerase II. About ten of the loops form a helical radial array of 250-nm diameter around the core of the chromosome. Further winding of this helix into a tight coil 700 nm in diameter, as at the top in (C), forms a metaphase chromatid. From Manuelidis91.

Figure 27-11 (A) Human chromosomes after one replication in the presence of 5-bromodeoxyuridine (BrdU). Both chromatids of each chromosome contain BrdU in one strand of the DNA duplex and normal thymidine in the other. (B) After two replications in the presence of BrdU one chromatid of each chromosome contains BrdU in both strands of the duplex and stains strongly with a special differential staining procedure. The other chromatid contains only normal thymidine in one strand of the duplex and is not stained. Courtesy of Carolina Biologicals.

Figure 1-3. Partial karyotypes of Giemsa-stained human chromosomes showing various manifestations of the fragile X site (arrows) a chromatid break (a), an isochromatid gap (b), a chromosome break (c), and endoreduplication (d).

A plot of x versus y results in the CIE chromatid ty diagram (Figure 6-6). When the chromaticities of all of the spectral colors are placed in this graph, they form a line called the locus. Within this locus and the line connecting the ends, represented by 400 and 700 nm, every point represents a color that can be made by mixing the three primaries. The point at which exactly equal amounts of each... 

Figure 25.2. Sister chromatid exchange formation. For differential staining of the sister chromatids, bromodeoxyuridine (BrdU) is incorporated into repheating DNA in place of thymidine (TdR). The solid line represents the original TdR-containing DNA strand and the dotted line represents the DNA strand containing BrdU. An SCE is shown to occur at the first S phase (S ) but will be observed at the second mitosis (Ml, l> ).

Figure 19.1 During the metaphase of cell division, a chromosome becomes two sister chromatids attached at the centromere. Chromosome banding exemplified using human chromosome 17.

Figure 19.9. Structure of colchicine. The biophore A (bold, see Fig. 19.8) is responsible for the therapeutic effectiveness. Toxicophore B (see Fig. 19.10 shown in bold) is responsible for the induction of sister chromatid exchanges (SCE) in vivo. Removal of toxicophore B or its replacement be isopropoxy groups abolishes the induction of SCEs without affecting the therapeutic potential.

Figure 8.6 Example of a human metaphase figure showing several sister chromatid exchanges (indicated by...

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