The quantitative analysis of chromosome pairing and chiasma formation based on the relative frequencies of M I configurations

Whilst reliable estimates of chiasma frequencies can usually not be obtained, the probability (b) of a chromosome arm to be bound by at least one chiasma can often be determined. In the absence of interference this probability equals (1–e ^–2), where 2 is the average chiasma frequency of the chromosome arm and the average crossover frequency or map length. In the presence of interference is shown to retain its genetic meaning as an additive metric that may describe the chromosome arm or other distinctive chromosome segment in terms of genetic recombination. It is a form of potential map length, comparable to, but numerically different from the regular map length. It is termed provisionally crossing-over potential.A chromosome with armsm andn with crossing-over potentials and will form ring bivalents with a frequency (1–e ^–2).(1–e ^–2); open bivalents with a frequency (1–e ^–2).e ^–2+(1–e ^–2).e ^–2; univalent pairs with a frequencye ^–2.e ^–2. Estimates of these frequencies yield equations from which and may be solved. In rye (Secale cereale) their ratio (q) is approximately two and differs from the mitotic arm length ratio of 1.4, indicating localization of chiasmata in the long arms.Graphs are given to show how, with constantq, the relation between the probabilitiesb _m andb _n of the two arms being bound changes with changing averageb.Data are presented on chiasma frequencies in M I, and compared with the frequencies expected in the absence of interference to give an impression of the degree of interference. Apparent fusion of chiasmata simulates interference.     

Chiasma distribution in Truxaline grasshoppers

Similar patterns of chiasma distribution are found within the individual arms of the chromosome complement in four species of Truxaline grasshopper. There is a linear relationship between chiasma frequency and chromosome arm length although the telocentric elements have a consistently higher mean number of chiasmata per unit of arm length. The positions of successive chiasmata can be defined in terms of residual (r.c. and r.t.) and interference (T) distances which vary in value according to both arm length and chiasma frequency. There is a tendency for one chiasma to lie in a distal position which is accentuated when additional chiasmata form. Supernumerary B chromosomes do not appear to influence the overall control mechanism of chiasma distribution. There is no indication that bivalents within a nucleus compete for chiasmata nor does the chiasma distribution in one arm of the metacentric members influence that in the other. It is suggested that the control of chiasma formation is determined mainly by interference factors.     

Monotelodisomics in pearl millet

Summary In the progeny of crosses between plants with the chromosome number 2n=13+2 telocentrics as the male parents and the normal diploids of Pennisetum typhoides S. & H., two plants with 2n=13+1 telocentric chromosome were located. These two plants were heterozygous for an interchange, since at diakinesis and metaphase I associations of four chromosomes were observed. These plants had a chromosome constitution of 2n=13+t (or 6+tI); one chromosome of a homologous pair was represented by a telocentric chromosome so was monosomic for one arm, that is, these plants were monotelodisomics (Kimber and Sears, 1968).     

Polymerization Sites in the D-Domain of Human Fibrin(ogen)

The present work deals with localization of previously unknown polymerization sites of the fibrin DD-fragment. D-dimer we obtained has a pronounced inhibitory effect on fibrin polymerization (IC₅₀ = 0.06 M). The inhibitory effect of the D-fragment disappeared after reduction and carboxymethylation. However, polypeptide chains _DD (B134-461) and _DD (63-411)₂ of the DD-fragment, isolated by preparative electrophoresis, displayed their inhibitory activity. For instance, the rates of fibrin protofibril lateral association were decreased twice in the presence of _DD and _DD chains at their molar ratios to fibrin of 0.40 and 0.15, respectively. The IC₅₀ values for _DD and _DD were 0.24 and 0.10 M, respectively. Highly specific inhibition of protofibril lateral association suggests that the protofibril lateral association sites are located in B134-461 and 63-411 regions of the fibrin D-domain. Our data confirm those reported by Doolittle et al. regarding the -chain and a hypothesis about -chain of fibrin D-domain (Yang, Z., Mochalkin, I., and Doolittle, R. F. (2000) Biochemistry, 97, 14156-14161).     

NADH dehydrogenase: a new molecular marker for homoeology group 4 in Triticeae. A map of the 4RS chromosome arm in rye

Summary Structural gene loci encoding the monomeric isozymes nicotin adenin dinucleotide dehydrogenase (NADH dehydrogenase or NDH) have been located on the 4AL, 4B, and 4DS chromosome arms of Triticum aestivum cv Chinese Spring, on the 4RS chromosome arm of Secale cereale cultivars Imperial, King II, Dakold, and Ailes, on the 4S¹ S/7S¹ chromosome of Aegilops longissima, the 4E of Elytrigia elongata, and the CSU-A of Aegilops umbellulata. All the results support the homoeologous relationships among these chromosomes in the five species studied. In addition, a map of the 4RS chromosome arm in cv Ailes has been realized, linking loci Pgm-1 (located on the 4RS chromosome arm) and Ndh-1 (17.91 cM), with an estimated distance between both loci and the centromere of 20.00 cM and 32.12 cM, respectively.     

A strongly fluorescing abnormal chromosome in a malformed child

Summary The case of a sexchromatin negative girl with multiple malformations is presented. A small metacentric chromosome was found to replace her second X chromosome, half of which was strongly fluorescing after staining with Quinacrinedihydrochloride, and late replicating after labelling with tritiated thymidine. The chromosome was interpreted as a translocation chromosome between the long arms of a Y and a partially trisomic autosome.     

1H NMR studies of the mercuric ion binding protein MerP: Sequential assignment,secondary structure and global fold of oxidized MerP

Summary The oxidized form of the mercuric ion binding protein MerP has been studied by two-dimensional NMR. MerP, which is a periplasmic water-soluble protein with 72 amino acids, is involved in the detoxification of mercuric ions in bacteria with resistance against mercury. The mercuric ions in the periplasmic space are first scavenged by the MerP protein, then transported into the cytoplasm by the membrane-bound transport protein MerT, and finally reduced to elementary (nontoxic) mercury by the enzyme mercuric reductase. In this work, the ¹H NMR spectrum of oxidized MerP (closed disulfide bridge) has been assigned by using homonuclear 2D NMR techniques. The secondary structure and global fold have been inferred from the nuclear Overhauser effect (NOE) data. The secondary structure comprises four -strands and two -helices, in the order ₁₁₂₃₂₄. The protein folds into an antiparallel -sheet, ₂₃₁₄, with the two antiparallel helices on one side of the sheet. The folding topology is similar to that of acylphosphatase, the activation domain of porcine pancreatic procarboxypeptidase B, the DNA-binding domain of bovine papillomavirus-1 E2 and the RNA-binding domains of the U1 snRNP A and hnRNP C proteins. However, there is no structural similarity between MerP and other bacterial periplasmic binding proteins.     

Absence of chiasmata from the heteromorphic region of chromosome I during spermatogenesis in Triturus cristatus carnifex

Analysis of squash preparations of spermatocytes from crested newts, Triturus cristatus carnifex, has shown that in most cells at least one large bivalent regularly fails to form chiasmata in one arm-pair. Feulgen microphotometry of diplotene and metaphase bivalents has shown that it is the largest bivalent in each cell which shows chiasma failure in one arm-pair. A C-banding technique which identifies chromosome I by virtue of a long, darkly stained region in its long arm, was used to confirm the absence of chiasmata from one arm-pair of the longest bivalent, and specifically from the darkly stained region. The achiasmate region which chromosome I exhibits during spermatogenesis, corresponds to the heteromorphic region of oocyte lampbrush bivalent I in which chiasmata never form. A possible correlation between the complete absence of crossing-over from the heteromorphic region and unusual cytological and molecular features which it exhibits, are discussed.     

Interrelationship between chromocentres and chiasmata in radish (Raphanus sativus L.)

A comparative study of the number and distribution of chromocentres in interphase nuclei and mean chiasma frequency at diakinesis has been made in three varietal populations of radish (Raphanus sativus L.), Scarlet Globe, Japanese White and Chinese White. The study showed a significant difference between the varietal populations in mean chiasma frequency and number of chromocentres (P<0.001), indicating that these nuclear characters are genotypically controlled. The correlation analysis revealed a significant negative correlation between chromocentres and chiasma frequency (r= -0.87). It was concluded that an increase in the amount of constitutive heterochromatin, as inferred by chromocentre counts, adversely affects the chiasma frequency and, consequently, genetic recombination in radish.     

A feature extractor for curvilinear patterns: a design suggested by the mammalian visual system

Summary A feature extractor for a pattern recognizer which can effectively process curvilinear drawings has been synthesized and simulated on a digital computer.The design of the network was suggested by the visual system of higher animals — especially the structure of the receptive fields of cortical neurons. This feature extractor is a multilayered parallel network composed of analog threshold elements. It consists of six layers in cascade. The first layer is a two-dimensional array of photoreceptors. The second layer is a contrast-detecting layer, each element of which has an on-center-type receptive field. The third one is a line-detecting layer. An element of this layer corresponds to a simple cortical cell, and responds to lines whose orientation is proper for the element. Each element has a receptive field consisting of an elongated excitatory region flanked on either side by inhibitory regions. The fourth layer is also a line-detecting layer, but each element, which corresponds to a complex cell, is not sensitive to the exact position of the line. An element of the fifth layer, which may correspond to a hypercomplex cell, responds when the line detected in the preceeding layer is curved. In the final layer, the curvature of the line is detected regardless of the orientation of the line, that is, an element of this layer gives an output approximately proportional to the curvature of the line presented in its receptive field.     

Quantitative comparisons between the karyotypes of Australian marsupials from three different superfamilies

Relative DNA values and percent lengths of chromosome arms have been studied for six species of the super-family Dasyuroidea, five species of Phalangeroidea and four species of Perameloidea. By multiplying by relative DNA values all percent lengths have been expressed in the same units. Two species are said to share a chromosome if neither of the arms differs at the 5% level of probability. It is argued that if species share at least two two-armed chromosomes, this can be taken as evidence of relationship. A standard dasyurid karyotype has been defined and individual species of Dasyuridae show only small deviations from it. The nature and significance of the bi-modal distribution of chromosome numbers in marsupials is discussed.     

Effects of retinoids on porcine thyrocytes under different culture conditions

The purpose of the paper was to study the morphological effects of retinoids on non-transformed cells such as thyrocytes. The formation of follicles was studied in primary cultures of porcine thyrocytes by adding retinol and thyroid stimulating hormone (TSH) to cells grown in the absence of TSH to form monolayers. The proliferation and apoptosis of thyrocytes were studied in cells both grown adherent to plastic surfaces and in suspension. Standard medium with traces of retinol and the same medium without retinol were used. Retinol alone was added to thyrocytes grown in the absence of TSH (TSH culture) or both retinol and TSH were added to cultures after stimulation with TSH (TSH culture). The concentration was varied from 0 to 80M for retinol and from 0 to 13M for retinoic acid. At a concentration of 13M, the effect of retinol was similar to that of retinoic acid. At concentrations higher than 40M, retinol reduced the formation of thyroglobulin-immunoreactive follicles, whereas up to 13M retinoic acid had no obvious influence on follicle formation. The retinoids induced apoptosis under all experimental conditions. In contrast, a significant decrease in proliferation and in the formation of thyroglobulin-immunoreactive follicles was observed only in adherent cells cultured in customary medium. The decrease in functional follicles after treatment with retinol suggests a de-differentiating effect of retinoids on normal thyrocytes and is in contrast with the differentiating effect of retinoids observed in cancer cells.     

Chiasma distribution in rye chromosomes of diploid rye and in wheat/rye addition lines in relation to C-heterochromatin

Summary In five genetically different inbred lines of rye and in the seven Chinese Spring/Imperial wheatrye addition lines, chiasma distribution in rye chromosomes was studied with respect to the amount and position of constitutive heterochromatin (Giemsa C-bands). In all inbred lines, rye chromosomes with one primary terminal band were more frequently found as univalents than those with primary bands on both telomeres. These chromosomes were most probably 5R and/or 6R. In the addition lines a highly significant reduction in the number of arms bound by chiasmata was found for rye chromosomes 5R and 6R. Because of the similar chiasma distribution in the inbred lines and in the rye chromosomes of the addition lines, no effect of the wheat genome on the number of chiasmata in the rye chromosomes can be ascertained. However, a relationship between chiasma frequency and chromosome arm length seems to exist, since under reduced chiasma conditions the two shortest arms of the rye complement, those of chromosomes 5R and 6R, frequently fail to form a chiasma. No effect of the large blocks of constitutive heterochromatin in the telomeres of the rye chromosomes on the position of chiasmata within a bivalent could be established.This study was financially supported by the Deutsche Forschungsgemeinschaft     

Complete characterization of a large marker chromosome by reverse and forward chromosome painting

Marker chromosome are small supernumerary chromosomes that are sometimes associated with developmental abnormalities. Hence, the genes involved in such cases provide an interesting approach to understanding developmental abnormalities in man. As a first step towards isolating such sequences, marker chromosomes need complete characterization. By combining chromosome isolation by flow sorting and the degenerate oligonucleotide primed — polymerase chain reaction, we have constructed a DNA library specific for a marker chromosome found in a child with severe developmental abnormalities. We used fluorescent in situ hybridization of the library onto normal metaphase spreads (reverse chromosome painting) and were thus able to determine that the marker consists of the centromeric part of chromosome 7, the telomeric region of the long arm of chromosome 5 and the telomeric region of the short arm of the X-chromosome. Subsequently, we hybridized normal chromosome-specific libraries of the relevant chromosomes onto metaphases containing the marker chromosome (forward chromosome painting) and could in this manner establish the precise location of the different chromosome regions on the marker chromosome itself. This is a general approach suitable for outlining marker chromosomes in detail, and will aid the identification of the genes involved.     

Assignment of human ferritin genes to chromosomes 11 and 19q13.3→19qter

Summary Extracts of hamster-human and mouse-human hybrids, some with translocations involving chromosome 19, have been assayed for both human spleen ferritin (rich in L subunits) and human heart ferritin (rich in H subunits). Hybrid lines retaining part of the long arm of chromosome 19 including the region 19q13.319qter produced human L type ferritin. This confirms the previous assignment of the ferritin gene to chromosome 19 (Caskey et al. 1983). However, lines retaining chromosome 11 were found to contain human H type ferritin suggesting that the gene for the H subunit is on this chromosome. The presence of chromosome 6 was not necessary for the expression of either H or L type human ferritin. It thus seems unlikely that the gene for idiopathic haemochromatosis is a ferritin gene.     

Immunochemical study of transforming growth factor-β in the kidney of the rat and chicken

Transforming growth factor- (TGF-) is a homodimeric polypeptide of 25 kDa, which regulates cell growth and differentiation and influences extracellular matrix metabolism. Using immunochemical techniques, we identified TGF- in the loops of Henle and the collecting and Bellini ducts of rat kidney and in the loops of Henle of chicken kidney. Furthermore, we detected two TGF--immunoreactive proteins on kidney blots of the rat of 12.5 and 47 kDa, and three on chicken kidney blots of 12.5, 34, and 47 kDa. We suggest that the precursor forms of rat and chicken TGF-2 or 3, chicken TGF-4, and the mature form of all of them are expressed in the collecting and Bellini ducts of rat kidney and the loops of-Henle of rat and chicken kidney.     

Chromosome patterns and nuclear phenomena in the cycad families Stangeriaceae and Zamiaceae

The chromosome karyotypes are described and scale diagrams prepared of 35 species representing 8 genera of the cycad families Stangeriaceae and Zamiaceae. The karyotype patterns, chromosome types and characteristics of the nucleolar organisers and heterochromatin are discussed in relation to their evolution in this ancient group of plants. A possible path of chromosome evolution is suggested by the concurrence in some genera of terminal heterochromatic knobs on chromosome arms and a single pair of telocentric homologues which in the remaining genera are replaced by complex partially heterochromatic nucleolar-organising chromosomes. — It is suggested that telocentric chromosomes may be of ancient origin in the cycads and that there may have been a progression from telocentric to mesocentric karyotypes. The paucity of genera today and the taxonomic isolation of the cycads from the remainder of the present-day flora renders impossible the corroboration of this theory by direct cytological comparisons with other groups.     

Non-reciprocal gonadal dysgenesis in hybrids of the chironomid midge Chironomus thummi

In male hybrids of the cross Chironomus thummi thummi (stock Hl) x Ch. th. piger (stock E) , but not the reciprocal cross, rudimentary testes develop at a growth temperature of 21 ° C. Within the dysgenic testes of these hybrids a number of abnormalities are observed which are restricted to the germ line. Approximately 60% of the hybrid males show allocyclic chromosome behaviour in spermatogonia and spermatocyte I nuclei. Within these nuclei two groups of four chromosomes are formed which differ from one another in their state of condensation. Each chromosome group consists of three long and one short chromosome. In cases where allocycly is very pronounced, the chromosomes of both groups disintegrate into numerous unequally sized fragments at meiotic prometaphase I, and gametes are not produced. In individuals, in which the allocycly is less pronounced or absent the nuclear divisions appear to be normal but chromosome and chromatid aberrations are frequent, and the number of viable sperm is reduced. In these males, the chiasma frequency is also decreased more than 12-fold in comparison with the reciprocal, unaffected piger x thummi hybrids.     

A model for somatic pairing derived from somatic crossing over with third chromosome rearrangements in Drosophila melanogaster

Summary X-ray induced crossing-over between the left arms of third chromosome pairs heterozygous for rearrangements was used to measure the somatic pairing of these arms. mwh spots were scored in the wing blades. A significantly reduced number of crossover spots is found in flies heterozygous for inversions or translocations located in the 3L arm. This decrease from control frequencies was experimentally demonstrated to be due to inviability of some crossover spots which are aneuploid as a result of crossing-over within the inverted sequence or between the translocation piece and its centromere. By the same token, some euploid crossover spots are produced by crossing-over outside of the inverted region or between the translocation breakpoint and the mwh locus. Thus, these results are evidence that the euchromatic non-centric portions of the 3L arms are somatically paired in the presence of rearrangements.A model of somatic pairing in which chromosomes are normally found in a hair pin configuration is proposed to account for these results and for some previous results with X-chromosomes which indicated that inversion heterozygotes did not pair somatically.Supported in part by USPHS grant GM 16096 to J.R.M.     

The nature of the diversity of Antarctic fishes

The species diversity of the Antarctic fish fauna changed notably during the 40 million years from the Eocene to the present. A taxonomically restricted and endemic modern fauna succeeded a taxonomically diverse and cosmopolitan Eocene fauna. Although the Southern Ocean is 10% of the worlds ocean, its current fish fauna consists of only 322 species, small considering the global diversity of 25,000–28,000 species. The fauna is reasonably well-known from a taxonomic perspective. This intermediate designation between poorly known and well-known indicates that new species are regularly being described. A conservative estimate of the number of undescribed species is 30–60; many of these may be liparids. On the Antarctic continental shelf and upper slope the fauna includes 222 species from 19 families of benthic fishes. The most speciose taxa are notothenioids, liparids and zoarcids, accounting for 88% of species diversity. Endemism for Antarctic species is also, coincidentally, 88%, at least threefold higher than in faunas from other isolated marine localities. Eight notothenioid families, including five that are primarily Antarctic, encompass a total of 44 genera and 129 species, 101 Antarctic and 28 non-Antarctic. The 101 Antarctic species make up 45% of the benthic species diversity in the Antarctic region. However, at the highest latitudes, notothenioids contribute 77% of the species diversity, 92% of the abundance and 91% of the biomass. Although species diversity is low compared to other shelf habitats, the nature of the adaptive radiation in organismal diversity among notothenioids is noteworthy in the marine realm. In some notothenioid clades phyletic diversification was accompanied by considerable morphological and ecological diversification. The exemplar is the benthic family Nototheniidae that underwent a habitat or depth related diversification centred on the alteration of buoyancy. They occupy an array of pelagic and benthopelagic habitats at various depths on the shelf and upper slope. Diversification in buoyancy is the hallmark of the nototheniid radiation and, in the absence of swim bladders, was accomplished by a combination of reduced skeletal mineralisation and lipid deposition. Although neutral buoyancy is found in only five species of nototheniids some, like Pleuragramma antarcticum, are abundant and ecologically important. Much work remains to be done in order to frame and to use phylogenetically based statistical methods to test hypotheses relating to the key features of the notothenioid radiation. To reach this analytical phase more completely resolved cladograms that include phyletically basal and non-Antarctic species are essential.