Relation between the segregation of genetically conditioned signs and the segregation of induced cleft palate in fetus F2 hybrid generation.
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Abnormalities, Drug-Induced↗
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Results for “Segregation”
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Comparison of the segregation of the RYR1 C184OT mutation with segregation of the caffeine/halothane contracture test results for malignant hyperthermia susceptibility in a large Manitoba Mennonite family.
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Calcium Channels↗
Spatial organization of the peripheral input to area 1 cell columns. II. The forelimb representation achieved by a mosaic of segregates.
The view (advanced in the previous paper) that the topographic organization in the forelimb region of area 1 of Macaca fascicularis monkeys should be regarded as a mosaic of discrete units--segregates--is evaluated. It is found that in all cortical layers the RFs sampled within a single segregate possess a wide variety of sizes and configurations, and occupy a wide variety of positions on the skin relative to the segregate RF center (the latter is a small skin area common to RFs of all neurons in the segregate). This within-segregate RF variability is structured so that the position of RFs of neurons sampled from different sectors of a segregate exhibits little, if any, systematic shift. The skin area that provides sensory input to any given area 1 segregate (estimated by the aggregate of the RFs sampled from that segregate) is extensive. This 'segregate RF', however, is not homogenous: i.e. central regions of the segregate RF are included in the RFs of a higher fraction of the neurons in the segregate than are peripheral regions. Segregate RFs appear particularly extensive when their size is compared with a relatively small shift in skin position that takes place when one shifts from one segregate to the next. Consequently, the skin areas that provide the sensory inputs to neighboring segregates overlap to a very large degree; and even fairly remote segregates in area 1 can receive a substantial common input. The arrangement of segregate RFs in area 1 is, in general, somatotopic. Nevertheless, the local relationships that are obtained among different segregates can deviate significantly from a strictly somatotopic pattern. The area 1 topographic organization detected in this study appears to differ substantially from that described by other investigators. A more detailed analysis suggests that most of the major differences between this and the previous descriptions of area 1 organization may largely be attributable to the different experimental conditions employed, and that the results of this study and those described by workers using different mapping methods are, in fact, generally compatible. Finally, it is suggested that the mosaic pattern of the topographic organization detected in area 1 may reflect the bundled nature of its afferent input.
Animals↗
Residential segregation and the epidemiology of infectious diseases.
Several empirical studies have documented the effects of residential segregation on health inequalities between the US African-American and white populations. However, the majority of such studies have not explained the pathways that link residential segregation and specific health outcomes. This paper presents a conceptual framework of the role that residential segregation may play in the epidemiology of tuberculosis (TB) and other infectious diseases. This is an important issue given the concentration of TB cases among US racial/ethnic minorities and the increasing gap in the incidence of infectious diseases between minorities and the white majority. Segregation may have an indirect effect on the transmission of TB because of its negative impact on the quality of neighborhood environment in segregated communities. Segregation concentrates poverty, overcrowded and dilapidated housing and social disintegration in minority areas, and results in limited access to health care. Furthermore, two dimensions of residential segregation (isolation and concentration) may have direct effects on TB transmission. The isolation of minorities confines TB to segregated areas and prevents transmission to the rest of the population. High-density levels in minority areas increase the probability of transmission within the segregated group. In order to operationalize the above pathways, health researchers may rely on the segregation literature, which has conceptualized various dimensions of residential segregation and proposed ways to measure them. The indirect pathways that link segregation and TB can be captured through exposure indices, which quantify the concentration of risk factors for TB for various racial and ethnic groups. The direct pathways can be captured through the isolation index (which is a proxy for the degree of interaction between the segregated group and the rest of the population) and two proposed measures of density (which are proxies for the likelihood of transmission within the segregated group and from the segregated group to the rest of the population).
Communicable Diseases↗
Chromosomal regions associated with segregation distortion in maize.
Segregation distortion skews the genotypic frequencies from their Mendelian expectations. Our objectives in this study were to assess the frequency of occurrence of segregation distortion in maize, identify chromosomal regions consistently associated with segregation distortion, and examine the effects of gametophytic factors on linkage mapping. We constructed a simple sequence repeat (SSR) linkage map for a LH200/LH216 F(2)Syn3 (i.e., random-mated three times) population, and compared the segregation distortion in this map with the segregation distortion in three published linkage maps. Among 1,820 codominant markers across the four mapping populations, 301 (17%) showed segregation distortion ( P < 0.05). The frequency of markers showing segregation distortion ranged from 19% in the Tx303/CO159 mapping population to 36% in the B73/Mo17 mapping population. A positive relationship was found between the number of meioses and the frequency of segregation distortion detected in a population. On a given chromosome, nearly all of the markers showing segregation distortion favored the allele from the same parent. A total of 18 chromosomal regions on the ten maize chromosomes were associated with segregation distortion. The consistent location of these chromosomal regions in four populations suggested the presence of segregation distortion regions (SDRs). Three known gametophytic factors are possible genetic causes of these SDRs. As shown in previous research, segregation distortion does not affect the estimate of map distance when only one gametophytic factor is present in an SDR.
Journal Article↗
Lightness differences and the perceived segregation of regions and populations.
A striking finding reported by Beck, Sutter, and Ivry (1987) was that, in textures composed of regions differentiated by the arrangement (checks and stripes) of two texture elements (light and dark squares), a large lightness difference between the squares could fail to yield segregation between the regions, whereas a smaller lightness difference could sometimes yield strong segregation. In the experiments reported here, we compared the segregation of striped and checked arrangements of light and dark squares into regions with the segregation of two randomly interspersed populations of light and dark squares into subpopulations. Perceived lightnesses are the same for a given set of squares, whether they are arranged in regions or in intermixed populations. Perceived population segregation is approximately a single-valued function of the lightness differences of the squares, but perceived region segregation is not. The reason for the difference between population segregation and region segregation may be that region segregation is mediated by detectors' having large oriented receptive fields (large bar detectors) that are sensitive to the fundamental spatial frequency and orientation of the texture region as defined by the arrangement of the squares (Beck et al., 1987; Sutter, Beck, & Graham, 1989). These detectors cannot be responsible for population segregation, because the light and dark squares are distributed randomly throughout these patterns and therefore do not define a consistent arrangement of any particular spatial frequency or orientation. The light and dark squares in the population patterns fall equally on excitatory and inhibitory regions of large bar detectors. A plausible explanation for population segregation is to suppose that the segregation is the result of similarity grouping of the light and dark squares.
Contrast Sensitivity↗
Susceptibility to vinblastine-induced aneuploidy and preferential chromosome segregation during meiosis I in Robertsonian heterozygous mice.
Chromosome segregation at meiosis I was studied in oocytes and spermatocytes of four different Robertsonian (Rb) heterozygous mouse stocks by cytogenetic analysis of meiotic products. Two Rb heterozygotes spontaneously yielded high frequencies of unbalanced oocytes. In one case, Rb(2.18)Rma, the excess hyperploidy was mainly accounted for by nondisjunction of normal bivalents, suggesting a generalized impairment of meiotic segregation. In each stock, frequencies of hyperploid spermatocytes were either not significantly different or significantly lower than the corresponding frequencies in the oocytes. This confirmed the greater risk of segregational errors in female than in male carriers of the same Rb metacentric. The hypothesis that an error prone system of meiotic segregation, such as the trivalent configuration of single Rb heterozygous oocytes, could be hypersensitive to chemically induced malsegregation was tested by injecting Rb heterozygous females with low doses of vinblastine (VBL). An intraperitoneal injection of 0.06 or 0.09 mg/kg VBL before the first meiotic division significantly increased the spontaneous frequency of hyperploid oocytes, inducing segregational errors of both the trivalent and normal bivalents. The comparison of these data with VBL effects in B6C3F1 mice showed that single Rb heterozygous oocytes are more sensitive to VBL-induced meiotic aneuploidy than oocytes with a standard karyotype. Although segregation distortion has been repeatedly shown in the progeny of Rb heterozygous mice with a significant excess of all telocentric balanced offspring, it has never been demonstrated whether this is a primary event occurring during meiotic segregation or a consequence of selective postconceptional death. In this study, we showed that preferential segregation occurred during female meiosis in all the Rb stocks tested. When segregation distortion was analyzed separately in balanced and unbalanced oocytes, the latter did not show preferential segregation, suggesting that, when the two telocentrics segregated from each other, then the metacentric was randomly directed to the ovum or the polar body.
Aneuploidy↗
Marker segregation without chromosome loss at the emt locus in Chinese hamster cell hybrids.
Segregation, defined as the reexpression of the recessive phenotype, has been examined in Chinese hamster cell hybrids heterozygous at the recessive emtr locus. Segregants were selected in emetine, and the role of chromosome loss in the segregation process was evaluated by detailed karyotype comparison of segregants with their hybrid parent. In emtr CHO x emt+ CHO hybrids (CHO is thought to be hemizygous at the emt locus), segregants were obtained at high frequency, and no consistent chromosome loss was found in the segregants. In hybrids made with Emtr CHO and wild-type lines other than CHO (CHW,CHL,V-79), where two wild-type alleles are thought to be present in the hybrid, segregants were obtained at much lower frequency, consistent with a two-step segregation process. These segregants revealed consistent loss of one chromosome 2 or deletion of a part of the long arm of a chromosome 2. Thus, one step in segregation seems to be chromosome loss while the other step must have a different mechanism, possibly the same mechanism that operates in the CHO x CHO hybrids. Two major conclusions can be drawn: (1) the emt gene maps to a hemizygous region of the long arm of a chromosome 2 in Chinese hamster, and (2) a segregation mechanism other than chromosome loss appears to operate with high efficiency in intraspecific hybrids.
Aneuploidy↗
Telomere-mediated plasmid segregation in Saccharomyces cerevisiae involves gene products required for transcriptional repression at silencers and telomeres.
Plasmids that contain Saccharomyces cerevisiae TG1-3 telomere repeat sequences (TRS plasmids) segregate efficiently during mitosis. Mutations in histone H4 reduce the efficiency of TRS-mediated plasmid segregation, suggesting that chromatin structure is involved in this process. Sir2, Sir3 and Sir4 are required for the transcriptional repression of genes located at the silent mating type loci (HML and HMR) and at telomeres (telomere position effect) and are also involved in the segregation of TRS plasmids, indicating that TRS-mediated plasmid segregation involves factors that act at chromosomal telomeres. TRS plasmid segregation differes from the segregation of plasmids carrying the HMR E silencing region: HMR E plasmid segregation function is completely dependent upon Sir2, Sir3 and Sir4, involves Sir1 and is not influenced by mutations in RAP 1 that eliminate TRS plasmid segregation. Mutations in SIR1, SIN1, TOP1, TEL1 and TEL2 do not influence TRS plasmid segregation. Unlike transcriptional repression at telomeres, TRS plasmids retain partial segregation function in sir2, sir3, sir4, nat1 and ard1 mutant strains. Thus it is likely that TRS plasmid segregation involves additional factors that are not involved in telomere position effect.
Chromatin↗
Latino, Asian, and black segregation in U.S. metropolitan areas: are multiethnic metros different?
This study examines 1990 residential segregation levels and 1980-1990 changes in segregation for Latinos, Asians, and blacks in U.S. metropolitan areas. It also evaluates the effect of emerging multiethnic metropolitan area contexts for these segregation patterns. While black segregation levels are still well above those for Latinos and Asians, there is some trend toward convergence over the decade. More than half of the areas increased their Latino segregation levels over the 1980s, and almost three-fourths increased their Asian segregation levels. In contrast, black segregation levels decreased in 88% of metropolitan areas. Multiethnic metropolitan area context is shown to be important for internal segregation dynamics. Black segregation levels are lower, and were more likely to decline in multiethnic metropolitan areas and when other minority groups grew faster than blacks. Latino segregation was also more likely to decline in such areas, and declines in both Latino and Asian segregation were greater when other minority groups were growing. These findings point up the potential for greater mixed-race and mixed-ethnicity coresidence in the neighborhoods of multiethnic metropolitan areas.
Adult↗
Molecular cytogenetic detection of meiotic segregation patterns in sperm nuclei of carriers of 46,XY,t(15;17)(q21; q25).
Structural chromosomal abnormalities in gonadal tissue represent an important category of parentally transmittable unbalanced chromosomal abnormalities to the offspring. A child with multiple anomalies was sent for cytogenetic analysis, and his karyotype was 46,XY,der(17)t(15;17)(q21; q25). This abnormality was transferred from his grandfather to his father and to the proband. In this family, 5 persons (1 female and 4 male) are the carriers of this abnormality. In this study, fluorescence in situ hybridization (FISH) on sperm nuclei of 4 male carriers was studied to determine the distribution of segregation patterns of the balanced translocation 15q;17q. The segregation results showed that the segregation products in the third carrier (the grandfather) were different, but they were not statistically significant. The segregation patterns in the other carriers were similar. Overall, 50.3% of the sperm nuclei (mean value for 4 carriers) analyzed were the result of alternate segregation; 36.9%, of adjacent I segregation; 9.0%, of adjacent II segregation; and 2.4%, of 3:1 segregation; the remaining 1.3% could be diploid sperm nuclei or of 4:0 segregation. Multicolor FISH analysis appears to be a rapid and reliable method for the direct analysis of segregation patterns in sperm nuclei of carriers of balanced reciprocal translocation, and it also provides interesting information for determining the possible risks for the offspring.
Adult↗
Texture segregation in the cat: a parametric study.
We have investigated how different texture parameters affect texture segregation in the cat, and which strategies cats use to solve the segregation task. Five cats were presented with stimuli consisting of two adjacent panels. One side contained a square area of a particular texture embedded in a different background texture; the other side was filled with only the background texture. The animal's task was to detect at which side the texture difference was presented. Sensitivity for the texture difference was assessed by making one aspect of the texture (in most instances the size of the texture elements) dependent upon performance by means of a staircase procedure. Among the most prominent parametric effects are those of density and element position randomization. In general, segregation was optimal at intermediate densities and deteriorated at larger and smaller densities. Element position randomization caused a slight but systematic decrease in segregation performance. Furthermore, we found texture elements at the border between different textures to be of primary importance for segregation. Which strategy the animals used for solving the segregation task depended upon the presence of random figure/background reversals in subsequent stimulus presentations during training. The animals learned to detect texture differences if these reversals were present, and without reversals, they learned to identify the particular texture in the target square. Interestingly, parameter dependencies of segregation did not depend upon the detection strategy used. We have speculated that the two different strategies used by the cats to solve the segregation tasks are related to different hierarchical levels of texture segregation which can be traced back to different stages of texture processing in human models of segregation performance.
Animals↗
Caenorhabditis elegans DNA that directs segregation in yeast cells.
We have isolated seven DNA fragments from Caenorhabditis elegans that enhance the mitotic segregation of autonomously replicating plasmids in the yeast Saccharomyces cerevisiae. These segregators, designated SEG1-SEG7, behave like isolated yeast chromosomes: they increase the stability and simultaneously lower the copy number of circular plasmids during mitotic growth in yeast. During meiosis, plasmids containing the C. elegans segregators show higher levels of precocious or aberrant disjunction than do plasmids bearing isolated yeast centromeres. Yet one of the segregators improved the meiotic segregation of the parental plasmid. We estimate that there may be as many as 30 segregator sequences in the C. elegans genome, a value that is consistent with the polycentric nature of C. elegans chromosomes. Five of the seven segregators are linked to sequences that are repeated in the worm genome, and four of these five segregators cross-hybridize. Other members of this family of repetitive DNA do not contain segregator function. Segregator sequences may prove useful for probing the structure of centromeres of both C. elegans and S. cerevisiae chromosomes.
Animals↗
Segregation of recombinant chromatids following mitotic crossing over in yeast.
It has long been assumed that chromatid segregation following mitotic crossing over in yeast is random, with the recombinant chromatids segregating to opposite poles of the cell (x-segregation) or to the same pole of the cell (z-segregation) with equal frequency. X-segregation events can be readily identified because heterozygous markers distal to the point of the exchange are reduced to homozygosity. Z-segregation events yield daughter cells which are identical phenotypically to nonrecombinant cells and thus can only be identified by the altered linkage relationships of genetic markers on opposite sides of the exchange. We have systematically examined the segregation patterns of chromatids with a spontaneous mitotic exchange in the CEN5-CAN1 interval on chromosome V. We find that the number of x-segregation events is equal to the number of z-segregations, thus demonstrating that chromatid segregation is indeed random. In addition, we have found that at least 5% of the cells selected for a recombination event on chromosome V are trisomic for this chromosome, indicating a strong association between mitotic recombination and chromosome nondisjunction.
Alleles↗
Induced chromosomal exchange directs the segregation of recombinant chromatids in mitosis of Drosophila.
In meiosis, the segregation of chromosomes at the reductional division is accomplished by first linking homologs together. Genetic exchange generates the bivalents that direct regular chromosome segregation. We show that genetic exchange in mitosis also generates bivalents and that these bivalents direct mitotic chromosome segregation. After FLP-mediated homologous recombination in G2 of the cell cycle, recombinant chromatids consistently segregate away from each other (x segregation). This pattern of segregation also applies to exchange between heterologs. Most, or all, cases of non-x segregation are the result of exchange in G1. Cytological evidence is presented that confirms the existence of the bivalents that direct this pattern of segregation. Our results implicate sister chromatid cohesion in maintenance of the bivalent. The pattern of chromatid segregation can be altered by providing an additional FRT at a more proximal site on one chromosome. We propose that sister chromatid exchange occurs at the more proximal site, allowing the recombinant chromatids to segregate together. This also allowed the recovery of reciprocal translocations following FLP-mediated heterologous recombination. The observation that exchange can generate a bivalent in mitotic divisions provides support for a simple evolutionary relationship between mitosis and meiosis.
Animals↗
Segregation of recessive phenotypes in somatic cell hybrids: role of mitotic recombination, gene inactivation, and chromosome nondisjunction.
Somatic cell hybrids heterozygous at the emetine resistance locus (emtr/emt+) or the chromate resistance locus (chrr/chr+) are known to segregate the recessive drug resistance phenotype at high frequency. We have examined mechanisms of segregation in Chinese hamster cell hybrids heterozygous at these two loci, both of which map to the long arm of Chinese hamster chromosome 2. To follow the fate of chromosomal arms through the segregation process, our hybrids were also heterozygous at the mtx (methotrexate resistance) locus on the short arm of chromosome 2 and carried cytogenetically marked chromosomes with either a short-arm deletion (2p-) or a long-arm addition (2q+). Karyotype and phenotype analysis of emetine- or chromate-resistant segregants from such hybrids allowed us to distinguish four potential segregation mechanisms: (i) loss of the emt+- or chr+-bearing chromosome; (ii) mitotic recombination between the centromere and the emt or chr loci, giving rise to homozygous resistant segregants; (iii) inactivation of the emt+ or chr+ alleles; and (iv) loss of the emt+- or chr+-bearing chromosome with duplication of the homologous chromosome carrying the emtr or chrr allele. Of 48 independent segregants examined, only 9 (20%) arose by simple chromosome loss. Two segregants (4%) were consistent with a gene inactivation mechanism, but because of their rarity, other mechanisms such as mutation or submicroscopic deletion could not be excluded. Twenty-one segregants (44%) arose by either mitotic recombination or chromosome loss and duplication; the two mechanisms were not distinguishable in that experiment. Finally, in hybrids allowing these two mechanisms to be distinguished, 15 segregants (31%) arose by chromosome loss and duplication, and none arose by mitotic recombination.
Animals↗
Segregation products of male mice doubly heterozygous for the RB(6.16) and RB (16.17) translocations: influence of sperm karyotype on fertilizing competence under varying mating frequencies.
The meiotic segregants of male mice heterozygous for Rb(6.16)24Lub and Rb(16.17)7Bnr were viewed, for the first time, at first cleavage metaphase. Chromosomes were analyzed after G-banding, C-banding, and karyotyping. To study sperm aging effects, chromosomes of 202 one-cell zygotes derived from males mating at intervals of approximately 3, 14, and 21 days were examined. At least 89.6% of sperm-derived complements were products of 2:2 segregation; at most, a possible 6.4% were 3:1 segregants. The six expected types of 2:2 segregants, both balanced and unbalanced, were equifrequent in the total zygote population derived from sperm of all ages. When the data were analyzed according to mating frequency, the 3-day sperm population considered most likely to be fresh showed a deficiency of the segregant nullisomic for chromosome 6 and disomic for chromosome 17, when compared with the reciprocal segregant (P less than 0.025) as well as to all other 2:2 segregants (P less than 0.05). However, these sperm fertilized in greater numbers (P less than 0.01) than their reciprocal segregant (disomic for 6 and nullisomic for 17) in the 14-day sperm population. While sperm with chromosomal abnormalities are capable of fertilization, the competence of segregants nullisomic for 6 and disomic for 17 apparently depends on the prior storage period in the male. Further, the results suggest that the effect of aneuploidy on sperm function is dependent on the specific chromosome(s) involved.
Aneuploidy↗
Pedigree analysis of plasmid segregation in yeast.
We have used pedigree analysis to investigate the mitotic segregation of circular and linear DNA plasmids in Saccharomyces cerevisae. Circular ARS plasmids, which bear putative chromosomal replication origins, have a high segregation frequency and a strong bias to segregate to the mother cell at mitosis. The segregation bias explains how the fraction of plasmid-bearing cells can be small despite the high average copy number of circular ARS plasmids. Linear ARS plasmids do not show strong segregation bias, nor does the 2 mu ori-containing plasmid YEp 13, when it is present in strains containing intact 2 mu circles. In the absence of endogenous 2 mu circles, YEp 13 behaves like an ARS plasmid, showing a strong maternal segregation bias. The presence of a centromere on circular ARS plasmids eliminates segregation bias. We discuss a model for plasmid segregation, which explains these findings and the possible biological significance of mother-daughter segregation bias.
DNA↗