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PubMed1990

Development of abnormal lamination and binocular segregation of retinal afferents onto the rat superior colliculus.

Unilateral optic tract lesions made in newborn rats produce abnormal retinotectal pathways on the opposite side. The present investigation was designed to study the development of the abnormal retinal projections in the superior colliculus using anatomical tracing methods. The aberrant uncrossed retinotectal pathway develops within the first postnatal week. In spite of this, the retraction of the crossed projection, which indicates binocular segregation, is of late onset. This indicates that the induced segregation of retinal inputs is not dependent on regressive events such as ganglion cell death and terminal field retraction. These data and the results of lid-suture experiments are consistent with a role for spontaneous retinal activity in the regulation of the plasticity of retinal projections to the rat superior colliculus.

Animals↗
PubMed1977

Application of the transfection technique for segregation of avian tumor viruses.

The possibility of clong avian tumor virus (ATV) by the transfection technique was studied. The attempts required efficient facilitator for the uptake of exogenous cellular DNA by chick embryo cells (CEC) to increase transfection efficiency. The calcium method was more efficient than the DEAE-dextran method for the uptake of tritium-labeled DNA, and the calcium method was used in further segregation studies of ATV by transfection of cellular DNA from ATV-infected cells. The test viruses included the BAI-A strain of avian myeloblastosis virus (a mixture of subgroup A and B viruses) and the B77 strain of avian sarcoma virus (a mixture of transforming and transformation-defective viruses). Analysis of the recovered progeny viruses after transfection revealed that they were indeed segregates of the parent viruses.

Animals↗
PubMed1990

Duplication 16q12----qter arising from 3:1 segregation in a 46,XX,t(13;16) (q12;q12) mother.

A congenitally abnormal female baby was found to have the karyotype 46, XX, +der (16) t (13; 16) (q12;q12) mat. GTG, QFQ, CBG, THA and Ag-NOR banding techniques allowed the identification of the abnormal chromosomes in the proposita and in the translocation carriers through three generations. Duplication 16q resulted from 3:1 segregation in the carrier mother. The hypothesis of a specific meiotic segregation for this translocation is discussed. The phenotypic effects of proximal 16q duplications are analysed together with other four reported cases, which have similar duplicated segment and no other relevant chromosomal abnormality.

Abnormalities, Multiple↗
PubMed1990

Commingling and segregation analysis of blood pressure in a French-Canadian population.

Commingling and segregation of age-sex-adjusted systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial blood pressure (MBP) were examined in 1,560 individuals from 374 French-Canadian nuclear families. After correction for skewness, evidence in favor of two commingled distributions was found for SBP in the combined data (parents and offspring) and in parents, but not in offspring. Segregation analysis (using the computer program POINTER) suggested that a multifactorial contribution to all three phenotypes was greater in offspring than in parents, which could be the result of either polygenic or shared environmental components relevant to sibships, or both. Statistical evidence was found for a major effect on SBP. However, Mendelian transmission of the major effect was rejected, and no transmission of the major effect (equal tau's) was not. This is just the opposite to what would be expected if the major effect was due to a major gene, and it would ordinarily be considered as sufficient evidence to refute a major gene effect on SBP. However, the commingling in parents but not in offspring (who are all below 26 years of age), and the finding of equal transmission probabilities (nearly equal to 1), are compatible with an alternative interpretation. It is possible that there is a real major gene effect on SBP but that the genotype for elevated SBP has not yet expressed itself in the offspring as they have not yet gone through the risk period. Accordingly, this possibility needs to be evaluated further in additional studies involving older offspring.

Blood Pressure↗
PubMed1990

Segregation analysis of idiopathic torsion dystonia in Ashkenazi Jews suggests autosomal dominant inheritance.

The results of segregation analysis applied to a family study of idiopathic torsion dystonia in Ashkenazi Jews are reported. The study is based on 43 probands (with age at onset prior to 27 years) from 42 nuclear families; pedigrees were extended systematically through all available first- and second-degree relatives, who were directly examined and videotaped. Final diagnoses were based on exam information and blinded videotape review. Segregation analysis demonstrated that the data are consistent with autosomal dominant inheritance with 30% penetrance. Recessive and polygenic inheritance were strongly rejected. There was no evidence for sporadic cases or new mutations. The high incidence and dominant inheritance of early-onset idiopathic torsion dystonia in Ashkenazi Jews suggests genetic homogeneity within this population, making it especially useful for linkage studies of this disorder.

Adolescent↗
PubMedDate not supplied

Unexpected nonrandom mitochondrial DNA segregation in human cell hybrids.

Cells from patients with various inherited mitochondrial myopathies have been reported to contain more than one type of mitochondrial DNA (heteroplasmy). It has been suggested that the degree of heteroplasmy may be important in the clinical manifestations of these diseases; however, little is known about the origin or inheritance of organellar heteroplasmy in mammalian cells. In order to gain an understanding of mechanisms of genetic transmission of mitochondrial DNA, we have made somatic cell hybrids by fusion of cells containing mitochondrial DNA with differences in their restriction endonuclease patterns. This permits the artificial mixing of mitochondria and the study of mitochondrial DNA segregation patterns. In this report evidence will be presented to show that there are differences in the propagational abilities of mitochondrial genomes in many intraspecies human cell hybrids crosses. This was unexpected since it is generally believed that mitochondrial DNA is under relaxed cellular controls and that random transmission of mitochondrial DNA to daughter cells occurs at mitosis. Mitochondrial DNA from tumorigenic HeLa cells, which is initially present in somatic cell hybrids made by fusion of HeLa cells to nontumorigenic cells, is usually lost after several weeks of continuous cell culture. However, when HeLa cells are fused to other tumorigenic cells, random mitochondrial DNA segregation occurs. Thus the tumorigenicity (perhaps state of differentiation) of the parental cells used in these fusions often correlates with the type of mitochondrial DNA retained.

DNA, Neoplasm↗
PubMed1990

Combined segregation and linkage analysis of genetic hemochromatosis using affection status, serum iron, and HLA.

Characterizing the distribution of parameters of iron metabolism by hemochromatosis genotype remains an important goal vis-à-vis potential screening strategies to identify individuals at genetic risk, since a specific marker to detect the abnormal gene has not been identified as yet. In the present investigation, we analyze serum iron values in ascertained families using a method which incorporates both segregation of the clinical affection status and the HLA linkage information to identify the underlying genotypes. The analysis is performed using an extension of the model presented by Bonney et al., comprising regressive models for segregation analysis and the multipoint linkage strategy implemented in LINKAGE. The gene was found to be completely recessive with respect to both clinical manifestations and serum iron abnormalities, with significant differences in expression by sex. Clinical manifestations were present for all male homozygotes in this data set, suggesting that the recessive hemochromatosis genotype is fully penetrant at all ages in males. This was not the case for younger females. Significant genotype-specific age and sex effects were found for serum iron values. It is interesting that deletion of the HLA marker information did not affect our ability to resolve the genetic model when we analyzed a bivariate phenotype. This serves as a reminder that a search for relevant biological markers can be equally important in discerning the genetic etiology of a disease trait, as a search for linked genetic markers.

Age Factors↗
PubMed1989

Models for positional signalling with application to the dorsoventral patterning of insects and segregation into different cell types.

Models of pattern formation and possible molecular realizations are discussed and compared with recent experimental observations. In application to the dorsoventral patterning of insects, it is shown that a superposition of two pattern-forming reactions is required. The first system generates the overall dorsoventral polarity of the oocyte, the second generates the positional information proper with a stripe-like region of high concentration along the ventral side of the embryo. A single reaction would be insufficient since the two reactions require different parameters. The model accounts for the orientation of the DV axes of the oocytes in the ovary of Musca domestica and Sarcophaga, independent of the DV axis of the mother, for the formation of several ventral furrows in the absence of the primary gurken/torpedo system in Drosophila, as well as for the good size regulation of the dorsoventral axis as observed in some insect species. Segregation of a homogeneous cell population into different cell types requires autocatalytic processes that saturate at relatively low concentrations and nondiffusible substances responsible for the autocatalytic feed-back loops. Thus, these loops can be realized directly on the gene level via their gene products, for instance, by the mutual repression of two genes. A balance of the two cell types is achieved by a long-ranging substance interfering with the self-enhancing process. This substance is expected to have a more or less homogeneous distribution. This model accounts for the reestablishment of the correct proportion after an experimental interference and the change of determination after transplantation. Applications to the segregation of pre-stalk and prespore cells in Dictyostelium and of neuroblast cells from the ventral ectoderm in Drosophila are provided.

Animals↗
PubMed1989

Segregation of genetic hemochromatosis indexed by latent capacity of transferrin.

A genetic analysis of the segregation of hereditary hemochromatosis, indexed by the measurement of latent capacity of transferrin (LCAP), was undertaken in an ascertained sample of 147 pedigrees from Brittany, France. There were no mean differences by sex in the distribution of LCAP in the control sample, although in the family data there was a higher representation of males with low values than of females with low values, consistent with the higher proportion of affected males. The results of bivariate segregation analysis revealed no systematic evidence for heterozygous expression either in the biochemical domain of LCAP abnormalities or in increased liability to overt symptomatic disease. Joint consideration of the quantitative variable with hemochromatosis affection status allowed clear resolution of a recessive single-gene inheritance pattern in these families.

Adult↗
PubMed1989

Integration of distributed cortical systems by reentry: a computer simulation of interactive functionally segregated visual areas.

A computer model based on visual cortex has been constructed to analyze how the operations of multiple, functionally segregated cortical areas can be coordinated and integrated to yield a unified perceptual response. We propose that cortical integration arises through the process of reentry--the ongoing, parallel, recursive signaling between separate maps along ordered anatomical connections. To test the efficacy of this reentrant cortical integration (RCI) model, we have carried out detailed computer simulations of 3 interconnected cortical areas in the striate and extrastriate cortex of the macaque. The simulated networks contained a total of over 222,000 units and 8.5 million connections. The 3 modeled areas, called VOR, VOC, and VMO, incorporate major anatomical and physiological properties of cortical areas V1, V3, and V5 but are vastly simplified compared with monkey visual cortex. Simulated area VOR contains both orientation and directionally selective units; simulated area VMO discriminates the direction of motion of arbitrarily oriented objects; and simulated area VOC responds to both luminance and occlusion boundaries in the stimulus. Area VOC is able to respond to illusory contours (Kanizsa, 1979) by means of the same neural architecture used for the discrimination of occlusion boundaries. This architecture also generates responses to structure-from-motion by virtue of reentrant connections from VMO to VOC. The responses of the simulated networks to these illusions are consistent with the perceptual responses of humans and other species presented with these stimuli. The networks also respond in a consistent manner to a novel illusion that combines illusory contours and structure-from-motion. The response synthesized to this combined illusion provides a strong argument supporting the need for a recursive reentrant process in the cortex. Functional integration of the simulated areas in the RCI model were found to depend upon the combined action of 3 reentrant processes: (1) conflicting responses among segregated areas are competitively eliminated, (2) outputs of each area are used by other areas in their own operations, and (3) outputs of an area are "reentered" back to itself (through lower areas) and can thus be used iteratively to synthesize responses to complex or illusory stimuli. Transection of the reentrant connections selectively abolished these integrative processes and led to failure of figural synthesis. The proposed model of reentry suggests a basis for understanding how multiple visual areas as well as other cortical areas may be integrated within a distributed system.

Animals↗
PubMed1989

Testing separate families of segregation hypotheses: bootstrap methods.

Aspects of the statistical modeling and assessment of hypotheses concerning quantitative traits in genetics research are discussed. It is suggested that a traditional approach to such modeling and hypothesis testing, whereby competing models are "nested" in an effort to simplify their probabilistic assessment, can be complimented by an alternative statistical paradigm - the separate-families-of-hypotheses approach to segregation analysis. Two bootstrap-based methods are described that allow testing of any two, possibly non-nested, parametric genetic hypotheses. These procedures utilize a strategy in which the unknown distribution of a likelihood ratio-based test statistic is simulated, thereby allowing the estimation of critical values for the test statistic. Though the focus of this paper concerns quantitative traits, the strategies described can be applied to qualitative traits as well. The conceptual advantages and computational ease of these strategies are discussed, and their significance levels and power are examined through Monte Carlo experimentation. It is concluded that the separate-families-of-hypotheses approach, when carried out with the methods described in this paper, not only possesses some favorable statistical properties but also is well suited for genetic segregation analysis.

Alleles↗
PubMed1986

On the power to detect differences between male and female mutation rates for Duchenne muscular dystrophy, using classical segregation analysis and restriction fragment length polymorphisms.

The power to detect departures from the theoretical proportion of new mutants in X-linked lethal disorders has been analyzed for several types of segregation analysis, including methods based on completely linked restriction fragment length polymorphisms. It is shown that all methods require large sample sizes in order to detect even large differences between male and female mutation rates. Ascertainment bias is shown to have a great effect on the outcome of the segregation analysis. All reviewed studies concerning the proportion of new mutants in Duchenne muscular dystrophy, whether they claimed equality or inequality between the male and female mutation rates, give insufficient evidence because of ascertainment bias and a too low power. An ascertainment bias-free method is given, with the advantage that information from many studies can be combined. By doing so, in the long run, even moderate departures from equality in mutation rates (if present) can be detected.

DNA Restriction Enzymes↗
PubMed1977

[Structure of the morphogenetic movements of gastrulation in Anura. I. Destabilization of ooplasmic segregation and cleavage under the action of clinostatic rotation].

The yolk segregation in the developing Rana temporaria egg was studied both in vivo and under the effect of clinostate rotation, i. e. slow rotation around the horizontal axis imitating the state of weightlessness. From the moment of fertilization and during the whole period of cleavage the yolk was shown to subdivide succesively in distinct phases which differ by the characteristic value of yolk granules. During the normal development, in spite of the marked variability of form and mutual position of phases, the main elements of their animal-vegetative order are preserved. Under the effect of clinostate rotation the process of normal segregation becomes destabilized and variations in the egg structure are expressed by the beginning of gastrulation in the diversity of variants of distribution of the cellular material competent to different morphogenetic movements.

Amphibians↗
PubMed1987

Segregation distortion in Rh polymorphism.

Segregation distortion for the Rh system is reported. Mother-infant pairs (1018 pairs) from maternity service divisions of government hospital and 216 complete families with a total of 692 children, of Visakhapatnam (Andhra Pradesh, South India) were typed for the D-d alleles of Rh system. The segregations analysis made by means of the T matrix method of ITO matrices, assuming Hardy-Weinberg equilibrium, reveals that: Rh-positive mothers produce fewer Rh-negative children with significance and Rh-negative mothers produce more Rh-positive children with less significance than expected in both the mother-child and family studies. This results in a reduction in the d allele from mothers to their children. Known Rh antigenic specificities and reproductive compensation do not explain the observed distortion. Other selectively acting forces probably linked to Rh compatibility system seem to be operating to gain d alleles to maintain Rh polymorphism.

Female↗
PubMed1988

A segregation and linkage study of classical and nonclassical 21-hydroxylase deficiency.

The segregation of classical and nonclassical 21-hydroxylase deficiency (21-OHD) and its linkage to HLA-B was investigated in 220 families. First, the surprisingly high frequency of the nonclassical 21-OHD gene estimated elsewhere was confirmed using a different methodology which avoided particular assumptions concerning the classification of an individual's genotype. In the present study the gene frequency was found to be .103 +/- .020 in an ethnically pooled sample and was as high as .223 +/- .062 among Ashkenazi Jews. Second, the segregation analysis of families ascertained through a nonclassical 21-OHD proband and those ascertained through a classical 21-OHD proband showed essentially identical results. A partial recessive model with no recombination between 21-OHD and HLA-B fitted the data better than did a complete recessive model with approximately 0.5% recombination between 21-OHD and HLA-B. The support for the partial over the complete recessive model depended on the assumed ascertainment probability, an unknown parameter in these data. Four families provided most of the evidence against the complete recessive model. All these included an unaffected sib who shared both HLA-B specificities in common with the affected proband. Possible explanations for the condition in these families include recombination, gene conversion, mutation in one of the parental gametes, or technical errors.

Adrenal Hyperplasia, Congenital↗
PubMed1987

Cell lineage segregation during bursa of Fabricius ontogeny.

The population dynamics of myeloid and lymphoid lineages during bursa of Fabricius ontogeny were analyzed by immunofluorescence by using two monoclonal antibodies (mAb). CL-1 mAb reacts with all chicken hemopoietic cells, except mature erythrocytes. L22 mAb reacts with bursa and bursa-derived lymphocytes, with a minor subset of macrophages and with some cells of the thymic medulla. The staining of embryonic bursas by these antibodies helps to distinguish between two different lineages of hemopoietic cells: CL-1+/L22+ cells represent B lymphocytes and a minor subset of macrophages, while CL-1+/L22- cells correspond to most of the macrophages and to the granulocytes, which disappear at the end of the embryonic life. CL-1+/L22- as well as CL-1+/L22+ cells were first observed outside the bursal rudiment. This indicates that there is a pre-bursal segregation between these two hemopoietic lineages and that two different kinds of precursors colonize the bursal rudiment at about the same time (day 9 for CL-1+/L22- cells and days 9 or 10 for CL-1+/L22+ cells). Moreover our data show that the colonization of the bursal epithelium by hemopoietic precursors is a two-step phenomenon. The first cells which enter belong to the CL-1+/L22- lineage, express Ia-like antigens at a high level, are dendritic in morphology, and represent cells of the macrophage/dendritic cell lineage. They are responsible for the formation of the epithelial bud which are then colonized by a small number of lymphoid precursors which belong to the CL-1+/L22+ lineage. Quail-chick bursa grafting experiments were also performed and the grafts were examined for CL-1 (restricted to chicken hemopoietic cells) and L22 reactivity. These observations confirmed our previous findings about the kinetics of the colonization of bursal rudiment by hemopoietic precursors and give support for a pre-bursal segregation between two hemopoietic pathways.

Age Factors↗
PubMed1987

[Genetic analysis of the polyauxotrophy of the early mitotic progeny of Saccharomyces cerevisiae zygotes. III. The behavior of the chromosome-III markers in polyauxotrophic clones and their mitotic and meiotic segregants].

Cloning and segregation analysis of polyauxotrophic (PA) progeny, as well as the study of diploid segregants, revealed an unusual state of the diploid genome in these strains. Analysis of linkage markers of chromosome III in all crosses may be expected to illuminate relationships between the homologous chromosomes. All PA strains were assigned to two major classes. In the class of PA strains with recombinant chromosome III, the effect of approachment of third linkage markers was noted. In other strains, transposition of genetic marker metA1 to chromosome III and its linkage to leu2 were discovered. The present study has demonstrated that the unusual state of the diploid genome of PA strains induces multiple nonspecific alterations in chromosome relationship and structure. It is likely that these alterations are the consequence of disturbance in mitotic apparatus of cell.

Chromosomes↗