Crossover Value Research Articles

Crossing of low-lying electronic levels of high-spin ferrous ion in deoxyhemoglobin and deoxymyoglobin

The electronic structure of high-spin S  2 ferrous ion in deoxy forms of hemoglobin and myoglobin is considered in terms of spin Hamiltonian formalism. Spin Hamiltonian parameters of the second order B 0 (2)( D), B 2 (2)( E) and, for the first time in the available literature, of fourth order B 0 (4), B 2 (4) and B 4 (4), are calculated for the rhombic symmetry case of Fe 2+. The Hamiltonian matrix is diagonalized for several sets of B ( k) q parameters compatible with other experimental data. The low-lying Fe 2+ levels exhibit crossings in a high magnetic field, applied along the z-axis perpendicular to the heme plane. The cross-over values of the magnetic field are determined to be H c1 = 46 kOe and H c2 = 168 kOe for D = 5.2, E = 0.6 cm −1 (close to the magnetic data of Nakano, N., Otsuka, J. and Tasaki, A. (1972) Biochim. Biophys. Acta 278, 355–371) and with B (4) 0 = 0.037, B (4) 2 = 0.005, B (4) 4 = 0.013 cm −1 and g z = 2.028. Experimental techniques for measurement of the crossing effects are discussed.

Genetic analysis of enzyme polymorphisms in plaice (Pleuronectes platessa)

Genetic analysis was performed on five enzyme systems (G3PDH; GPI-A; GPI-B; PGM; MDH-A) in plaice (Pleuronectes platessa) collected in spawning condition from the North Sea. Conventional crosses, induced gynogenesis and induced triploidy were performed. The data conclusively demonstrated the inheritance of isozymes by co-dominant alleles at individual loci for each system. No linkage was observed but tests did not include MDH nor the possibility of linkage between G3PDH and GPI-A. Some anomalous segregation ratios were observed, particularly a deficiency of heterozygotes for GPI-A, but the data were largely in conformity with Mendelian expectations. At the PGM locus, five independent anomalous individuals were scored and interpreted as mutations with a mutation rate of 1.1 X 10(-3) per gamete. Recombination with the centromere was assessed and induced triploidy and cross-over values of 41 per cent for PGM, 19 per cent for MDH-A and 9 per cent for GPI-B were derived on the assumption of complete interference. Amongst the parent fish, genotypic and phenotypic frequencies were largely consistent with the expectations of the Hardy-Weinberg Law, and allelic frequencies were not significantly different between year of collection or location of collection ground.

Linkage between a basic gene for anthocyanin pigmentation and a complementary gene for purple septum in rice (Oryza sativa L.)

Twelve characters showed segregation for pigmentation in the rice cross T-141xK-44-1. Inheritance was complicated by the involvement of the unusual number of genes ranging from two to five with different modes of action such as complementary, duplicate, inhibitory, anti-inhibitory etc. F2 ratios in respect of ten out of twelve characters are reported for the first time. Analysis of the combined segregation data revealed the existence of a pleiotropic basic gene responsible for the formation of purple pigment in eleven characters. This basic gene designated as A (C) is linked with the complementary gene-Pm for purple pigmentation at the septum region with the cross-over value of about 11 per cent. This linkage group forms part of group III of Misro et al. (1966) corresponding to the ‘A’ linkage group of Takahashi (1963).

Linkage of the Genes SBM and WLO in Peas1

AbstractLinkage between the Pisum gene sbm (conditioning resistance to the pea seed‐borne mosaic virus) and wlo (conditioning deposition of wax on pea leaflets) was studied in the F2 generation. No crossovers were detected in four crosses, involving 323 plants, but two were found in a fifth cross, involving 398 plants. The combined data from all crosses gave a crossover value of 11.95%, indicating that sbm is in Pisum linkage group VI.

CROSSING OVER AND DIPLOID EGG FORMATION IN THE ELONGATE MUTANT OF MAIZE

Rhoades (1941) found recombination in the proximal regions of chromosome 5 to be higher in male than in female flowers. Two explanations were proposed to account for the lower female values, namely: (1) there is a basic difference in rates of crossing over in mega- and microsporocytes, or (2) selective orientation of the chromosome 5 bivalent on the meiotic spindle leads to the preferential segregation of noncrossover chromatids to the basal megaspore. These alternatives have been tested by carrying out a half-tetrad analysis of the diploid eggs produced by plants homozygous for the recessive elongate (el) allele. The A2-Bt crossover values determined from the diploid eggs of elongate plants were much lower than those calculated from haploid sperm of both El el and el el plants. Since male and female flowers should have similar cross-over values if the orientation hypothesis were correct, it was concluded that the amount of crossing over in the A2-Bt region of chromosome 5 is intrinsically higher in male than in female meiocytes. In the analysis of diploid eggs the use of the Bt locus, which marks the centric region of chromosome 5, provided information on the origin of diploid eggs. The genotypic constitution of 425 diploid eggs was ascertained. Of these, 20.4% were Bt bt. They could not be accounted for by failure of the second meiotic division or by replication during the interphase between the two meiotic divisions, but are expected if there is a single division with an equational separation of the centromere regions of chromosome 5. The Bt Bt and bt bt genotypes arise from a disjunctional separation. It is proposed that diploid eggs are produced by an abnormal meiosis in which there is one division with either disjunctional or equational separation. Disjunctional separation is more frequent but the ratio of the two types varies from ear to ear. Recombination in the A2-Bt-Pr region of chromosome 5 was found to be higher in the haploid gametes of elongate homozygotes than in El El and El el plants. On the other hand, crossing over was reduced in the Sh-Bz segment of chromosome 9 in elongate plants, but the adjacent Bz-Wx interval was unaffected.

Tandem duplications in Drosophila melanogaster II. Meiotic pairing and exchange in heterozygous tandem duplications

In heterozygous females of tandem duplication Dp(1; 1) Gr, y(2) (w(-)spl sn(3)) (w(c) sn(3)) the frequency and distribution of exchange events were measured by the phenotypically different F1 recombinants. In comparison with wild type chromosomes the crossover values were strongly reduced within the heterozygous chromosome sections (between white and singed from 19.5 per cent to 2.1 per cent). Additionally, there was 0.24 per cent intrachromosomal exchange in the same chromosome section after the formation of a double loop (Fig.2). Crossing over was also reduced in both chromosome regions adjacent to the heterozygous duplication. A comparison of the conceivable pairing configurations with those configurations which are indicated by the recombinants gives an initial insight into the pairing behaviour of heterozygous tandem duplications during meiosis. The hypothesis of "polarized pairing" in Drosophila melanogaster is disproved by this kind of experiment.Crossover values within and adjacent to the duplication were also measured in heterozygous tandem duplications differing in the genetic length of their duplicated section. Here, meiotic pairing behaviour was found to depend on the genetic length and other parameters of the duplicated section. Conceivable sources for the different kinds of behaviour are discussed.

The direct-indirect transition in In1− xGaxP

Data (300°K) are presented on laser quality liquid phase epitaxial (LPE) In 1− x Ga x P, grown on lattice-matched {100} GaAs 1− y P y substrates, confirming a theoretical account presented by Altarelli that the direct-indirect transition occurs at x c ≈ 0.74. Photoluminescence data show that crystals ranging in composition from x = 0.52 to x = 0.70, all of which operate as lasers at 77°K, exhibit the same decrease in luminescence intensity from 77 to 300°K, indicating that x c > 0.70 at 300°K. The steep I–V characteristics (at 77 and 300°K) of Zn-diffused diodes prepared on crystals of composition x = 0.70 in contrast to the significantly more resistive behavior of x = 0.74 crystals is consistent also with the assignment x c > 0.70. The Λ band edge (300°K), determined by the photoluminescence data points, intersects the X band edge (300°K) at x c ≈ 0.74. A discussion, in terms of the problems inherent in In 1− x Ga x P crystals growth and quality, is presented to reconcile the difference in the crossover value ( x c ≈ 0.74) reported here on laser crystals and the lower value ( x c ≈ 0.63) of some other recent reports.

Inheritance and linkage relations of reaction to Xanthomonas phaseoli (E. F. Smith) Dowson (common blight), stage of plant development and plant habit in Phaseolus vulgaris L.

The inheritance of the reaction to Xanthomonas phaseoli (E. F. Smith) Dowson Nebraska isolate Xp-816, cause of common blight disease of beans Phaseolus vulgaris L. was studied in crosses between the late flowering, indeterminate, blight tolerant dry bean PI 207262 (Colombia) and susceptible cvs. GN 1140, an early flowering and indeterminate dry bean; Dark Red Kidney, a late flowering and determinate dry bean; and Gallatin 50, an early and determinate green bean. The tolerant disease reaction was dominant in the F1. A continuous distribution of disease reaction ratings, skewed in the direction of dominance, occurred in the F2 derived from the first 2 crosses while a slight bimodal distribution was observed in the F2 of the last cross. A low narrow sense heritability estimate of 14% was calculated by the regression of F3 progeny means on individual F2 plants, in the cross GN 1140×PI 207262. The occurrence of a small number of nonsegregating families in a low number of F3 families indicates that a small number of major genes were involved in controlling the disease reaction. Linkage did not appear to be involved between genes controlling early flowering (early maturity) and common blight tolerance. Coupling linkage occurred between genes controlling determinate plant habit and early flowering. A crossover value of 8.4% was estimated. Recombinants for early maturity, determinate habit, and blight tolerance were obtained. Transgressive segregation for early flowering and common blight susceptibility occurred in progeny derived from the cross of the two late-flowering blight tolerant lines, PI 207262 and GN Nebraska 1, sel. 27, indicating that the parents possessed different genes controlling these traits.

Inheritance and Linkage of Turnip Mosaic Virus and Downy Mildew (Bremia lactucae) Reaction in Lactuca serriola1

Abstract Data for resistance in Lactuca serriola L. to turnip mosaic virus (TuMV) and downy mildew were obtained from 5 F2 progenies of crosses between TuMV-susceptible, mildew-resistant, and TuMV-resistant, mildew-susceptible parents. The F1 progeny were TuMV and mildew-resistant. Of 1,103 F2 plants assayed 823 were TuMV-resistant and 280 TuMV-susceptible. A total of 834 mildew-resistant plants were observed, and 269 mildew-susceptible. Resistance to TuMV and mildew are each controlled by a single dominant allele, designated Tu and Dm, respectively. The TuMV gene, Tu tu, is linked with the mildew gene, Dm dm. In the repulsion phase, the crossover value was 12.0% ± 2.9. F2 progenies of crosses between TuMV-susceptible, mildew-resistant L. serriola and TuMV-susceptible, mildew-resistant L. sativa cv. ‘Calmar’ or ‘Imperial 410’, and crosses among cv. ‘Calmar’, ‘Imperial 410’, and ‘E-4’, indicated they possessed the same dominant allele for mildew-resistance, and the same recessive allele for TuMV-susceptibility.

THE INHERITANCE OF RESISTANCE TO PUCCINIA RECONDITA IN HEXAPLOID TRITICALE

Rob. ex. Desm. f. sp. tritici, was studied in the hexaploid triticale cultivars 6A-190, Rosner, Armadillo, Bronco, and Toluca 160.Resistance in the triticales studied was monogenically inherited and each cultivar carried a single dominant gene. The genes conditioned resistance to races 15 and 30, and were designated genes A (6A-190), B (Rosner) C (Armadillo), D (Bronco), and E (Toluca 160). Gene A was linked in repulsion with gene C with a crossover value of 44.75 ± 1.44% and segregated independently from the other genes. Genes B and C were also independently inherited. Gene B was not linked with genes C, D, and E but observed distorted ratios with genes D and E suggested the presence of a modifying gene or genes. A similar distorted ratio was observed between genes C and D. Gene C assorted independently from gene E. No recombinants were recovered from the cross between Bronco × Toluca 160 suggesting that genes D and E were allelic or closely linked. The parental triticale cultivars Bronco and Toluca 160 carrying the genes D and E, respectively, appeared to carry modifying genes which inhibited the expression of resistance in certain crosses.The result obtained indicated that the genes governing resistance were derived from the tetraploid wheat parental species and that resistance to wheat leaf rust carried by the rye parent was not expressed in the triticale amphiploid. It was also found that genes conditioning resistance to wheat leaf rust were equally effective in conditioning resistance to rye leaf rust.

A crossover suppressor-enhancer system in the mosquito Aedes aegypti.

A small reciprocal translocation T(1;2)1 involving chromosomes 1 and 2 and a paracentric inversion In(1)3 on m chromosome (1) of A. aegypti interact to give peculiar but consistent crossover values. The system is termed COSES and is associated with partial sterility. In females it suppresses crossing over tremendously to the right of bz and enhances crossing over to its left. In the males it enhances crossing over to the right of m (only 3 crossover units away from bz) hut the region to its left remains unaffected. COSES also displays interchromosomal effects by enhancing crossing over in linkage group III. Cytological and genetic evidence for the presence of translocation and inversion are presented. All three pairs of chromosomes are correlated to the three linkage groups.

Linkage of Turnip Mosaic Virus Susceptibility and Downy Mildew, Bremia lactucae, Resistance in Lettuce1

Abstract Data for resistance in Lactuca sativa L. to turnip mosaic virus (TuMV) and downy mildew were obtained from 8 F2 progenies of crosses between TuMV-susceptible, mildew-resistant, and TuMV-resistant, mildew-susceptible parents. The F1 progeny were TuMV and mildew resistant. Of 3,682 F2 plants assayed 2,773 were TuMV resistant and 909 TuMV susceptible. A total of 2,788 mildew-resistant plants were observed, and 904 mildew susceptible. Resistance to TuMV and mildew are each controlled by a single dominant gene, designated herein as Tu and Dm. The TuMV-susceptible gene, tu, is linked with the mildew-resistant gene, Dm. In the repulsion phase, the cross-over value was 12.5% ± 1.6.

Gonenkonkurrenz bei Oenothera unter dem Einflu\ eines gametophytisch wirksamen Gens in der ersten Koppelungsgruppe sowie ein Modell für die Untersuchung verzweigter Koppelungsgruppen

The progeny ratios obtained in male backcrosses of Oenothera hybrids to the complexes hookeri and flavens (identified by two marker genes and by the translocation break) showed statistically significant differences from Mendelian expectations.Presence of a gametophytic gene in the first linkage group is proposed. Its alleles ga (+) and ga (-) are thought to control development of the male gametophytes in such a manner that pollen grains carrying the different ga alleles and developing in a heterozygous female plant, will fertilize the female gamete with different average frequencies.A series of genetic models is developed, all taking into account the relative probability of the alleles ga (+) and ga (-) to function in fertilization, the probability of crossing over between the gene loci studied, and the branched configuration of the linkage group, due to the presence of the translocation.Based on these models, the relationships between the relative frequencies of the different classes of gametes are predicted for several theoretically possible arrangements of the genes within the linkage group.The models have general application for the localization of gametophytic genes and for the localization of genes in branched linkage groups.It turns out to be impossible to give an estimate for the disadvantage of ga (-) as compared to ga (+) from the backcross data alone. The empirical data permit only a combined estimate of the probabilities of fertilization by ga (-) and of crossing over between Ga and the locus of the marker gene.Comparison between the empirical data and the model makes it possible to determine the location of the marker loci and the locus of Ga with respect to one another. A branched linkage group appears most likely, but a linear arrangement in two chromosome arms cannot be ruled out.The observed cross-over values, and consequently, the map distances between the genes studied, are highly variable, both in different hybrids and in the progeny of a single hybrid.

Inheritance of resistance to powdery mildew Sphaerotheca macularis (Fr.)Jaczewski in the red raspberry, Rubus idaeus L.

The varieties Lloyd George and Burnetholm (and probably Malling Promise) are heterozygous for three genes governing resistance to mildew (S. macularis (FR.) Jaczewski, syn. S. humuli (DC.) BUrr.), Sp1 and Sp2 being dominant complementaries and sp3 recessive. Resistance whether of Sp1, Sp2 or sp3sp3 origin is epistatic to susceptibility. Sp3 is linked with the fruit colour gene T with a crossover value of ca. 25%, the gene order in this linkage group being B-Sx3-T-Sp3.Evidence suggesting linkage between H (hairy canes) and resistance is presented.

SPONTANEOUS CROSSING OVER IN THE MALES OF <i>DROSOPHILA</i> <i>ANANASSAE</i>: TWO-WAY SELECTION FOR RECOMBINATION VALUES

Spontaneous crossover values from males of D. ananassae showed great individual variation. From such a variable population two-way selection was started selecting randomly twenty heterozygous males from testcross progeny of a male with highest crossing over and from one with lowest values. Similar selection was continued for 15 generations. Wide variations in generation means were observed. The high line exceeds the low line significantly in mean crossover frequency. The difference in the two lines was established although the progressive increase was not significant. Since the difference in the two lines was established the effect of selection is genetic.

THE INHERITANCE OF ELECTROPHORETIC PATTERNS OF BLOOD ALBUMIN IN THE SILKWORM, <i>BOMBYX MORI</i> L.

Three heritable patterns, F, S and FS, of blood albumin in silkworm larvae were demonstrated by means of polyacrylamide gel electrophoresis. F type larvae were characterized by a single band which migrated more rapidly to the anode than that of the S type larvae. F1 hybrid between F and S strains showed an FS type characterized by having both zones, F and S. As a result of the mating experiments involving these phenotypes, it was found that these characters were controlled by a pair of codominant autosomal alleles, designated as AlbF and AlbS. It was clarified from linkage analysis that the allele was linked with narrow breast (nb) gene on the 20th chromosome with the crossover value of 6.2±1.02%.

Sex differences in recombination of linked genes in animals.

Reports of sex differences in crossing-over in animals, published since Haldane in 1922 suggested that crossing-over should be less frequent in the heterogametic sex, have been reviewed and discussed. No general rule is discernible apart from the absence of crossing-over in males of the dipteran generaDrosophilaandPhryneand in females of some lepidopteran species, due apparently to failure of chiasma formation in the heterogametic sex. In the majority of animal species examined crossing-over occurs in both sexes. While there is some tendency in mammals for crossover values in females to exceed those in males, it was of greater interest to find that marked sex-differences occur in the same species (data chiefly from the house mouse) in opposite directions in different chromosomes. The influence of factors acting locally in the chromosomes, such as those associated with hetero-chromatin, were indicated as promising subjects for the study of variations associated with sex.

CROSS-OVER VALUES IN THE SEX CHROMOSOMES OF THE MOSQUITO AEDES AEGYPTI AND EVIDENCE OF THE PRESENCE OF INVERSIONS.

CROSS-OVER VALUES IN THE SEX CHROMOSOMES OF THE MOSQUITO AEDES AEGYPTI AND EVIDENCE OF THE PRESENCE OF INVERSIONS.

SUPERVITAL MUTANTS OF ARABIDOPSIS

At three loci four phenotypically different mutations were induced by x rays which affect the photoperiodic response of the carrier. The standard wild type develops visible flower primordia in 10 to 12 days after germination. The mutants have various flowering response and may need a period up to 4 to 6 times as long for the completion of the same developmental stage. In spite of the large differences in the time required for the onset of fiowering, the life cycle of the latest mutant is only 2 to 3 times that of the wild type. The slower development is accompanied by very vigorous growth; dry matter production may increase over 20 times and seed production may rise tenfold. These hereditary changes do not involve impaired genetic transmission, altered crossing-over value or visible chromosomal alterations. In three different competitive populations (mutant x wild) under long-day conditions, in the greenhouse, during a 60-week period (about ten generations of the wild type), the mutant allele increased from the initial 0.500 frequency to 0.869, 0.995, and 0.997, respectively. The roughly estimated selective advantage of the mutants under the experimental conditions varies from 0.3 to over 1.0. These are extremely high values. Since the progressmore » of selection is rapid in self-fertilizing plant community, if vigorous late mutants occur at a fair rate, their rapid increase may be expected. In nature late ecotypes are prevalent. The possible evolution of the photoperiodic response in the species is discussed. The suggestion is made that the different degree of dominance of the late ecotypes, based on modifier genes, indicates the evolution of dominance of the character concerned and the late flowering forms in nature represent the emergence of the new wild type of the species. (auth)« less

Increased recombination from female Drosophila irradiated as larvae without oocytes.

Different x-ray doses to late third instar larvae of Drosophila produced elevated frequencies of crossovers only from eggs laid in the first week of the imagoes. Three broods from 8 to 21 day-old adults were homogeneous anaong control and three irradiation dosage groups. Comparison of noncrossover and crossover frequencies showed no evidence of radioresistant cells among the oogonia present in x-rayed larvae. Higher crossover and lower noncrossover values were found in the 14 to 21 day brood rather than in the earliest brood of the controls. This response of Drosophila and the lack of such response of Habrobracon to irradiation are discussed. (auth)