Single Interchange Research Articles

Uncertainties in dosemeter intercomparison techniques

The results of 180 intercomparisons of field dosemeters with an NPL secondary-standard exposure meter (type 2560, with a type 2561 chamber) have been analysed in order to study variations in readings when ionization chambers are interchanged during the comparison process. It is suggested that the percentage standard error of the mean of the combined series of chamber intercomparisons be used to set a target uncertainty (0.3%), action level (0.5%) and limit of acceptability (1.0%). The target uncertainty is consistent with IAEA estimates of uncertainty for this part of the calibration chain. It is shown that if the calibration procedure is repeated, the percentage difference between the geometric means calculated from each calibration (i.e. a single interchange of chambers) may be as high as . This reinforces the need for at least one repetition of the intercomparison procedure.

The skeleton of the symmetric traveling salesman polytope

The vertices of the skeleton of the symmetric Traveling Salesman Polytope are the characteristic vectors corresponding to the Hamiltonian tours in the complete graph K n with n ⩾3, and the edges of this skeleton are the 1-faces of the polytope. It is shown that this skeleton contains a Hamiltonian tour such that the Hamiltonian cycles in K n corresponding to two successive vertices differ in a single interchange, i.e., the interchange graph corresponding to the TSP-polytope is Hamiltonian. It is also shown that the skeleton can be covered by 1 2 ( n −2)! cliques, and has diameter at most n −3.

Cytogenetic studies on the interspecific hybrid Capsicum baccatum L.× C. frutescens L. and its progeny

Morphological and cytogenetical studies were carried out on the F1 and F2 hybrids and backcross derivatives of the interspecific cross Capsicum baccatum L. x C. frutescens L. The F1 and F2 hybrids displayed irregular meiosis with a maximum association of eight chromosomes in the former and one quadrivalent in the latter with the appropriate number of bivalents and univalents. It is inferred that C. baccatum differs from C. frutescens (yellow) by at least tow or three interchanges and from the white cultivar by a single interchange. Structural repatterning of chromosomes, erratic meiotic behaviour, genes for pollen sterility, segregational imbalances following intergenomic recombination are believed to be major factors causing sterility in the hybrids. The two species are sympatric and natural hybrids have not been realised.

On the penetration energy of slightly overlapping closed-shell molecules

In the one-determinant approximation to the general theory of intermolecular interactions, the single interchange term describing penetration of slightly overlapping closed-shell molecules is shown to be equivalent to order S 2 to the overlap energy resulting from suitably defined overlap densities of the individual molecules, supplemented by a term which vanishes exactly for Hartree-Fock wavefunctions of the separate molecules.

Intraspecific hybridization and its bearing on chromosome evolution inVicia narbonensis (Fabaceae)

Nine accessions ofVicia narbonensis, considered to be the wild progenitor of faba bean (Vicia faba), were investigated to ascertain the nature and extent of intraspecific karyotypic polymorphism. The chromosome complements resolved into four distinct types (A, B, C, D), and the meiotic data of F1 hybrids (A × B, B × C, A × C) revealed that alteration in chromosome morphology is the result of segmental interchanges. The interchange complexes indicate that the parents differ from each other by 1 to 2 interchanges. It is also evident that karyotype B, and not A as previously reported, is the normal karyotype of the species, and A and C are single homozygotes for unequal interchange. The comparative karyomorphology of the parents and the hybrids, and of two interchange heterozygotes of four chromosomes each in F1 hybrids of A × C shows that the chromosomes involved in the single interchange homozygotes (A, C) are not common and the breaks in both interchanges occurred in short and long arms of the involved chromosomes. Identification of the interchanged chromosomes in the complements and the frequency of ring and chain quadrivalents in the heterozygotes enabled location of the breakpoints. The present results provide probably the first example indicating that interchange homozygosity (A) is not only firmly established but also has enabled the species to spread further by adapting to a wide range of habitats. — The genetic relationships between A and D are very different. All seven chromosome pairs in D could be distinguished from A, and for that matter, B and C as well. From the meiotic pairing properties it is also amply clear that genome D is well differentiated from A and possibly B, and C, and deserves special status.

The orientation behaviour of multiple chromosome configurations in acridid grasshoppers

The existing data on the behaviour of multiple chromosome configurations arising from single interchanges between either metacentric–telocentric or telocentric–telocentric nonhomologues in 10 species of acridid grasshoppers are compared with data from four new cases. Two of these new cases involve metacentric–telocentric exchanges but the other two, for the first time in acridids, deal with a reciprocal translocation between two nonhomologous metacentrics. The combined data are used to evaluate the factors that influence multiple orientation in this family of grasshoppers and reemphasize the importance of chiasma frequency and chiasma distribution for multiple behaviour. This conclusion is reinforced by a consideration of the known cases of chain of three multiples originating from the Robertsonian fusion of nonhomologous telocentrics in acridoids. Key words: acridid grasshoppers, multiple chromosome configurations, chiasma distribution, orientation behaviour.

Chromosome configurations and sterility in intercrosses between homozygous interchanges involving same and different chromosomes in barley (Hordeum vulgare L.).

Chromosome configurations during meiosis and sterility were studied in intercross hybrids among 14 homozygous translocation lines in barley. The intercrosses included interchanges involving same and different chromosomes and one chromosome in common.1. Hybrids between translocations involving same chromosomes with breakpoints in similar arms showed ‘pair’ configurations and about 50% sterility.2. Hybrids between translocations where the arm carrying the break differed for one of the two chromosomes, showed _??_ 4 configurations and about 26% sterility.3. Single interchange heterozygotes showed _??_ 4 or Ch. 4 configurations and about 27% sterility.4. Frequency of alternate orientation decreased and sterility increased with increase in number of chromosomes involved in translocation.5. Sterility of intercross hybrids showing _??_ 6 and of those showing 2 _??_ 4 was similar. This sterility was approximately 50%.6. At AI, 8-6 and 7-1-6 separations were more frequent in the intercross hybrids which showed higher frequencies of adjacent orientations.

Direct calculation of intermolecular potential energy surfaces

A variation perturbation method is presented for the direct calculation of intermolecular interaction energies. The theory is based on valence bond ideas but avoids the full evaluation of the matrix elements by expansion in powers of interchange, a procedure which is valid for small overlap between the systems. The participating excited states are regarded as polarized pseudo-states and are determined by optimizing the long-range multipole-multipole part of the interaction energy. The validity of these ideas is illustrated by a calculation of the He-He interaction. A remarkable simplification is pointed out, in which the interaction energy is given almost exactly by the sum of the repulsive term, calculated as zero + single interchange, plus the long-range interaction.

On Detecting Total or Partial Symmetry of Switching Functions

This note presents a method for identifying total or partial symmetry of switching functions based on the application of the principle of residue test by numerical methods. The invariance of a switching function under a single interchange of two variables can be readily detected from the equality of some of the residues of expansion about these two variables. This procedure of detecting invariance is directly applied for the identification of total or partial symmetry of a switching function whose variables of symmetry may be either all unprimed (or all primed), mixed, or of multiform nature.

On detecting total and partial symmetry of switching functions

A method is presented for identifying total or partial symmetry of switching functions based on the application of the principle of residue test. The invariance of a switching function under a single interchange of two variables can be readily detected from the equality of some of the residues of expansions about these two variables. This procedure of detecting invariance is directly applied for the identification of total or partial symmetry of a switching function whose variables of symmetry are either all unprimed, all primed, or of mixed nature.

A New Method of Using Interchanges as Chromosome Markers1

A new method of utilizing interchanges as chromosome markers which will require one less than the n number of chromosomes to test the entire genome for linkage is proposed. The underlying principle is that each of the interchanged chromosomes in each stock would be marked by two widely separated breakpoints. Breeding procedures in maize for constructing a series with 2‐chromosome, double interchange stocks are described and illustrated by the results from a cross between two genetically marked T1‐5 interchange stocks. Breeding procedures for a series with 3‐chromosome, triple interchange stocks are described also.The detection of linkage with any major gene, using either the double or the triple interchange series should be much more efficient than tests using single interchanges. When heterozygous, many of the products of crossing over in the differential segments are deficient and hence not recoverable. Also only part of the recoverable crossovers are recognizable as recombinants.

Spontaneous interchange in Chorthippus brunneus

1. The meiotic behaviour of a male of Chorthippus brunneus (2n=16+X) is described whose germ-line was uniform in respect of a single interchange. 2. The sub-equal interchange was between a long, metacentric (L3) and the longest of the medium-sized acrocentric chromosomes (M4). The interchange points were equidistant from the centromere and the segments involved were at least as long as half the length of the arms involved. 3. Chains of four predominate. Chiasma formation was not observed in one of the interstitial segments and was uncommon in the other. The multiples showed only ca. 30% alternate orientation while adjacent homologous orientation was observed in over 50% of the cells. Chains with adjacent non-homologous orientation were not seen. 4. Although the relative frequency of adjacent homologous and adjacent non-homologous orientation recorded here is in the opposite direction to that found by Burnham in maize, the two sets of data are comparable because the structure of the chains is different in the two cases. 5. The role of structural changes and the probability of their becoming established is discussed. In this connection both their immediate prospects and their subsequent utility have to be considered. It is suggested that the maintenance of super-genes after crossing structurally different chromosome homozygotes may be more important than hybrid sterility in maintaining their genic dissimilarity. And protecting a super gene from recombination prior to its fixation in the homozygous condition may be more important in the origin of species than maintaining it by hybrid sterility afterwards.

Segmental Interchange in <i>Pisum sativum</i>

1. The relations between three different lines of Pisum sativum, the K line, the T line and the N lines, are discussed, with regard to chromosome structure. All three lines have seven pairs of chromosomes at meiosis. The K line when crossed with N lines was found by HAKANSSON to give a ring of four chromosomes at meiosis. Similarly the T line gives a ring of four chromosomes with N lines. The K line when crossed with the T line gives an association of 6 chromosomes at meiosis.2. This shows that the K line and the T line are related to N lines by a single interchange of chromosome segments and to each other by a double interchange, involving three chromosomes of the haploid set.3. Metaphase pairing is found to be due to chiasma formation, interstitial as well as terminal chiasmata being present at metaphase as in previously described Pisum plants.4. About 78% of the configurations of six chromosomes examined have an interstitial chiasma, the “median chiasma, ” between nonadjacent chromosomes of opposite parental complements. When this chiasma is present, the configurations assume the shape of a “figure-of-eight, ” similar to that described in Oenothera by DARLINGTON (1931).5. The presence of the “median chiasma” shows that an homologous interstitial segment is present in the otherwise non-homologous chromosomes taking part in it. A hypothesis is put forward to explain the origin of this segment.6. The “figure-of-eight” is shown to be a cytological demonstration of previous genetical crossing-over, on the single assumption that only homologous parts of chromosomes pair. This crossing-over gives segmental interchange between chromosomes only homologous in an interstitial region.7. As a result of this segmental interchange, there are four viable gametic types containing n-chromosomes possible, namely the two parental types and two new types containing the interchanged chromosomes. The different possible zygotic combinations to be obtained on selfing this plant are predicted. Instead of the progeny being restricted to plants with simple pairing and plants with associations of six chromosomes at meiosis, plants with rings of four chromosomes are expected, as a result of the new combinations resulting from segmental interchange.8. A re-examination of the ring of four chromosomes formed when the T line is crossed with N lines showed the presence of chiasmata on both sides of the attachment constriction in one pair of segments, in some cases. This demonstrates that the point of attachment is at some distance from the place where the change of segment occurs. It is suggested that such configurations occur also in Zea Mays and in Datura.The author desires to thank Miss C. PELLEW for supplying the material for cytological study, Dr. C. D. DARLINGTON and Dr. F. W. SANSOME for criticism and advice, and Mr. H. C. OSTERSTOCK for taking the photomicrographs and for assistance with the diagrams.