Chromosome distribution

The chiasma graph method (Wada and Imai, 1995) has been used to examine the frequency and chromosomal distribution of chiasma on... 

Fig. 1 Chromosomal distribution of Alzheimer s disease-related genes in the human genome...

Figure 7.26. Chromosome distribution of the H3 and LI bands. Ideogram of human chromosomes al 850-band resolution showing the position of the 1.1 (blue) and the H3 (red) bands as previously identified on the basis of the concentration of LI and H3 isochores, respectively. This figure shows that the gcnc-riohesi. GC-riohesl, H,3 bands are prevalently located distally on each chromosome arm and are generally not adjacent to the gene-poorcst, GC-poorest, bands, which are prevalently located more proximally. The in termed iate bands (M3, LI ) are lei) uncolorcd in order to emphasize this spacing. (From Saccone...

Figure 8.11. Chromosomal distribution of the 6591, rice F,ST sites. Genetic (left cMi and YAC-based physical (right kb) maps are shown for each chromosome. The solid liitcs across each chromosome show the positions and regions of YAC contigs on the genetic mitp. Different colors represent different F.ST densities observed on the individual contigs. (From Wu ct al., 2002).

The value of studying this heterogeneous group of mutations lies in the fact that they may arise by quite different processes. Some, such as translocations, probably result from a relatively direct effect of the mutagen on the genetic material others, such as aneuploids, could arise through interference with chromosome replication or chromosome distribution at mitosis. 

Aloni, Y., L. E. Hatlen, and G. Attardi. 1971. Studies of fractionated HeLa cell metaphase chromosomes. II. Chromosomal distribution of sites for transfer RNA and 5S RNA. J. Molec. Biol., 56 555-563. 

Chromosome maneuvers in mitosis lead to controlled chromosome distribution to the daughter cells. This makes an understanding of the cellular mechanism involved central to the problems of inheritance and development the perpetuation of the chromosome complement is a primary process on which all else depends. The range of disciplines interested in mitosis now extends to medicine because of recent studies on abnormal chromosome complements in man. But as usual, it is the intriguing complexity and beauty of the process itself which animates most researchers. 

Motion itself is considered here in a section separate from one on where chromosomes move, that is, on the mechanisms of controlled chromosome distribution. This artificial dichotomy reflects the separation of research activities on these two questions and underlines their equal importance for any complete understanding of mitosis. The general conclusion in each section is that the cytology and mechanics are well understood and that molecular hypotheses which at least are stimulating further research have now been formulated. A major assertion is that chromosome distribution can now be explained at the cytological level. 

Granted that the proposed explanation is at least reasonable for both meiotic and mitotic chromosome distribution, can the fundamental difference between these divisions also be explained As Ostergren (1951) proposed, a kinetochore structural difference may parallel the kinetochore orientation difference. An opposite polarity of sister kinetochores in mitosis has just been invoked to explain, in part, achievement of bipolar amphiorientation. On the same assumptions, if sister kinetochores lie close together and have a common polarity, their orientation to the same pole (syntely) should at least be facilitated. The required polarity occurs in the one example studied at late prophase (Amphiuma, p. 267). 

The distribution of chromosomes in meiosis is understandable in terms of initial orientation and reorientation. Direct evidence that initial orientation and reorientation are now explained at the cytological level comes from experiments on bivalents in which orientation and distribution are predictably altered the experimenter 1. can determine the distribution of any chosen chromosome 2. can induce unstable malorientation and 3. can stabilize malorientations and induce nondisjunction. The explanation offered is easily extended to chromosome distribution in mitosis and to most units other than bivalents in meiosis. Testable molecular hypotheses are readily suggested. These would relate features of the cytological explanations to the generally documented organizing center activity of kinetochores and to spindle fiber lability. 

Fig. 19. Diagrammatic representation of chromosome distribution in a bacterial cell according to the hypothesis of Jacob et al., 1963. A, Before replication the chromosome (above) and an episome (below) are shown attached to the cell membrane at sites depicted by filled circles. B, After replication, the daughter elements are attached to adjacent sites on the membrane. The arrows indicate where membrane growth is postulated. C, By the beginning of septation, membrane growth in the shaded area has separated one daughter chromosome and one episome Into each of the two new cells. (After Jacob et al. 1963. Cold Spring Harbor Symp. Quant. Biol., 28 329-348.)...

Hutchinson, J. and Lonsdale, L. M. (1982) The chromosomal distribution of cloned highly repetitive sequences from hexaploid wheat. Heredity 48,371-376... 

Vanderkooi, J. M. and Landesberg, R. In vivo synthesis of iron-free cytochrome C during lead intoxication. FEES Lett., 73, 254 Verlangieri, A. J. (1979). Prenatal and postnatal chronic lead intoxication and running wheel activity in the rat. Pharmacol. Biochem. Behav., 11, 95 Verschaeve, L., Driesen, M., Kirsch-Volders, M., Hans, L. and Susanne, C. (1979). Chromosome distribution studies after inorganic lead exposure. Hum. Genet., 49, 147... 

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