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PubMed2005

A case of selfish nucleolar segregation.

Mitotic segregation of nucleolus in fission and budding yeast proceeds without disassembling its complex structure, creating challenging problems for transmission of nucleolus-organizing regions during nuclear division. The SMC complex called condensin, which plays a leading role in organizing mitotic structure of chromosomes in all eukaryotes, is essential for nucleolar segregation in budding yeast, where rDNA chromatin is the main target of mitotic condensin activity. Mitosis-specific condensin targeting to the nucleolus presents an attractive model to study mechanisms controlling condensin binding to specific chromatin domains. Recent reports suggest that the early-anaphase release of Cdc14 from the nucleolus (FEAR pathway) controls the proficiency of nucleolar segregation by promoting the mitotic condensin function in rDNA. This finding uncovers an essential function for the FEAR pathway and postulates the unique nucleolar self-regulatory mechanism, which evolved to recruit two essential enzymatic activities, Cdc14 phosphatase and condensin ATP-dependent supercoiling, for the specific task of segregating nucleoli without their disassembly.

Adenosine Triphosphatases↗
PubMed2004

[Mapping by molecular markers showing segregation distortion].

The comparative analysis of segregation distortions of the codominant markers data presented in software MAPMAKER are made, where five RFLPs markers involve in a mouse F2 population with 333 individuals. The successive chi(2) test begins with the determinations of gametic or zygotic selection types, followed by the estimation of recombination fractions between two markers with the Newton-Raphson iteration method. It is better to use the molecular marker showing segregation distortion for constructing a genetic map, in the case of seriously skew segregation between both the adjoining markers. The successive chi(2) test provides better accuracy than that of classical chi(2) test for the estimation of the recombination values in F2 population with segregation distortion.

Animals↗
PubMedDate not supplied

Segregation, discrimination and mortality in U.S. blacks.

Theoretically, segregation and discrimination could affect mortality among blacks (African Americans) not only through their impact on social class (including the concentration of blacks in high-poverty areas) but also by influencing health care and psychosocial factors. This paper reviews evidence that variation in mortality rates for black infants and young adults living in large metropolitan areas is associated with the level of black-white segregation. A few metropolitan areas in California with relatively low levels of segregation are shown to have low black death rates and small black-white differences in mortality rates for infants and young adult males (15-44 years old). In-depth studies are needed in these areas. Longitudinal studies of potential "risk factors" for disease and death among blacks should include: personal histories of experiences with discrimination, psychological reactions to discrimination, segregation indexes, quality of life in residential areas, and social class indicators.

Adolescent↗
PubMed1999

Pattern formation by retinal afferents in the ferret lateral geniculate nucleus: developmental segregation and the role of N-methyl-D-aspartate receptors.

The projection from the retina to the lateral geniculate nucleus (LGN) in ferrets segregates during development into eye-specific layers and ON/OFF sublayers. The projection pattern and the morphology of single axons was examined at several postnatal ages. The axons progress from a simple, sparsely branched morphology at birth to crude arbors at postnatal day 7 (P7). At P14-P15, axons have terminal arbors that span one eye-specific layer. By P19-P21, retinal afferents in the A layers have segregated into inner and outer sublaminae that correspond to ON- and OFF-center cells. Sublaminae form mainly by directed growth of terminal arbors in appropriately positioned regions of the LGN, along with elimination of extraneous branches in inappropriate regions. From P28 to P35, the LGN assumes an adult-like shape, and retinogeniculate axons form terminal boutons on branch endings. During the period between P14 and P21, when retinogeniculate axons segregate into ON/OFF sublaminae, N-methyl-D-aspartate (NMDA) receptors were blocked with chronic infusion of specific antagonists into the LGN. NMDA receptor blockade prevents the retinal afferent segregation into ON/OFF sublaminae. Some individual retinogeniculate axons have arbors that are not restricted appropriately, and most are restricted in size but are located inappropriately within the eye-specific laminae. Thus, NMDA receptor blockade prevents the positioning of retinogeniculate arbors that lead to the formation of ON/OFF sublaminae in the LGN. These results indicate that the activity of postsynaptic cells, and the activation of NMDA receptors in particular, can influence significantly the patterning of inputs and the structure of presynaptic afferents during development.

2-Amino-5-phosphonovalerate↗
PubMed1999

Inclusion of risk factor covariates in a segregation analysis of a population-based sample of 426 breast cancer families.

Although many segregation analyses of breast cancer have been published, few have included risk factor covariates. Maximum likelihood segregation analyses examining age-at-onset (model 1) and susceptibility (model 2) models of breast cancer were performed on 426 four-generation families originally ascertained between 1944 and 1952 through a breast cancer proband. Cancer status and risk factor data were collected through interviews of participants or surrogates. When segregation analyses were performed on 10,791 women, without estimation of any covariates, all hypotheses under both models were rejected. Model 1, which required estimation of fewer parameters than model 2, provided a better fit to the data according to Akaike's Information Criterion. Further segregation analyses were performed under model 1 on a subset of women with complete data on education, age at first birth (nulliparous women included), and alcohol use, covariates that were found to significantly (P<0.05) improve the fit over the addition of exam age alone in logistic regression models. All three covariates improved the fit of the models, as did year of birth, but at all stages of model building, all of the hypotheses were still rejected. After the allele frequency was fixed at 0.0033, a subset of families appeared to fit a dominant model. Using this model, risk estimates were calculated based on inferred genotype, age, and covariate values. The penetrance was estimated to be 0.15, much lower than previous estimates based on families ascertained through breast cancer probands with early onset. Moreover, the estimates of penetrance were not greatly influenced by incorporation of the measured risk factors.

Adult↗
PubMed1990

Segregation distortion in inheritance of progressive rod cone degeneration (prcd) in miniature poodle dogs.

Segregation distortion was observed in inheritance of progressive rod-cone degeneration (prcd) in a colony of Miniature Poodle dogs. Breeding results, from both retrospective records and prospectively planned matings, were classified into five mating types: (1) affected to affected, (2) homozygous normal sire to any dam, (3) heterozygous to heterozygous, (4) heterozygous sire to affected dam, and (5) affected sire to heterozygous dam. For all but the last category, results were in accord with mendelian expectations for autosomal-recessive inheritance. However, litters of mating type 5 had fewer affected pups (20/77) than expected. The observed segregation ratio for this mating type (0.26) was significantly (P less than 0.001) less than the expected (0.50). The segregation distortion could not be accounted for by either pre- or postnatal loss of affected pups, as litter size and litter survivability were uniform among litters of different mating types. Either the prcd locus, or a linked locus, would appear to influence either gametic or zygotic fitness in the heterozygous mother. Comparison is drawn to the inheritance of retinitis pigmentosa in humans, in which decreased segregation ratios are also recognized.

Animals↗
PubMed1980

In vitro induction of segregational errors of chromosomes by natural cannabinoids in normal human lymphocytes.

It has been shown that segregational errors (SE) of chromosomes can be induced by olivetol and several halogenated inhalation anesthetics. The purpose of this study was to examine the effects of natural cannabinoids - including delta-9-tetrahydrocannabinol (THC), cannabinol (CBN), and cannabidiol (CBD) - on chromosome segregation. Lymphocytes obtained from healthy adult males were incubated with various concentrations of natural cannabinoids for 72 hours. Anaphase preparations were made from these cultures. A statistically significant increase in the incidence of SE of chromosomes was observed in the lymphocytes exposed to THC at a concentration of 3.2 x 10(-6) M, but not to CBN or CBD. A greater incidence of bridge formations, anaphase lags, micronuclei, and unequal segregations in bipolar divisions and multipolar divisions were observed in THC-treated lymphocytes, compared with the controls. However, only anaphase lags and unequal segregations in bipolar divisions reached statistically significant levels. It appears that THC affects the formation of microtubules and spindles and may be considered as a mitotic poison. The value of examining SE as a part of cytogenetic studies on chemical mutagens is emphasized. A description of a classification system of SE developed in our laboratory is also presented. This system can be applied to studies using both normal human lymphocyte cultures and lymphoid cell lines.

Adult↗
PubMed1984

The detection of major loci by segregation and linkage analysis: a simulation study.

Simulated multigenerational pedigrees were analyzed using the program GENPED and POINTER to examine the 1) limits of segregation analysis for detecting single locus, two-allele transmission of a dichotomous trait and 2) accuracy of the parameter estimates. Ten data sets of 30 pedigrees each (approximately 25 persons per pedigree) were simulated. The genotypic penetrance values were varied but the population prevalence of the trait was kept constant at 2%. For some data sets a linked marker locus was also simulated. Previous results had shown that a single major locus could be easily detected when the heterozygote penetrance (f1) was high or midway between the two homozygote penetrances. In this study, we found a single major locus could not be consistently detected by either method of segregation analysis when f1 was "low" to "intermediate." Accuracy of the parameter estimates depended on assumptions about the population prevalence. In those cases where the major locus could not be detected by segregation analysis, linkage to a marker locus could be detected as long as the marker was closely linked and there were not phenocopies in the population. Owing to the limited number of simulations in this study, we cannot generalize these findings. However, they provide a basis for further testing of methods of segregation analysis when factors such as the parameter values, family structure, and ascertainment scheme are varied.

Biometry↗
PubMed1987

Nonrandom segregation: uniformly most powerful test and related considerations.

When nonrandom segregation of marker haplotypes from parents to offspring is detected, leading to an increased parental haplotype sharing by affected offspring, an association between the disease and the marker loci is often inferred. In this paper, we provide the uniformly most powerful test for testing nonrandom segregation, and compare the power of this test with another test that is available in the literature. Other statistical properties of the two tests are also discussed. Further, since nonrandom segregation can result from linkage of the disease and marker loci, when the hypothesis of random segregation is rejected, it is of interest to estimate the underlying parameter assuming linkage. We provide an estimation procedure.

Biometry↗
PubMed1992

Segregation analysis of 159 soft tissue sarcoma kindreds: comparison of fixed and sequential sampling schemes.

In this study we compared parameter estimates and model hypotheses in pedigree data collected by fixed sampling with estimates and hypotheses derived by sequential sampling. Employing a fixed sampling scheme, we previously analyzed data on relatives of 159 childhood sarcoma patients. We have now extracted from that data set individuals who would have been included in a sequentially sampled study. We applied segregation analysis to the truncated data, to determine the mode of inheritance and major locus parameter estimates. With data from both sampling schemes we made a family-by-family comparison to determine each family's contribution to a major gene model. The two sampling schemes yielded similar results: we detected segregation of a dominant major gene and obtained similar major locus parameter estimates. However, the sequential sampling scheme derived these conclusions from data on 982 relatives rather than the 2,451 ascertained in the fixed sampling scheme. The sequential sampling scheme failed to identify only one of the kindreds likely to be segregating the gene. For this data set, the sequential sampling scheme would have provided an efficient mechanism to discriminate genetic hypotheses and would have permitted focus of resources on the specific kindreds likely to segregate a major gene.

Adolescent↗
PubMed1995

Phenotypic assortative mating in segregation analysis.

A model of phenotypic assortative mating was developed for application in segregation analysis. The model assumed a constant spouse correlation across the range of a quantitative trait or the liability to a discrete trait. Four traits were analyzed to evaluate: 1) the feasibility of applying likelihood analysis to pedigree data in order to distinguish between assortative mating and shared environmental effects as the source of spouse correlation; and 2) the impact on segregation analysis of the failure to account for either assortative mating or shared environmental effects, as appropriate. Height ratio (the ratio of sitting to standing height) and eye color comprised the traits for which the observed spouse correlation reflected assortative mating; serum cholesterol and peptic ulcers (with genotypes defined by the ABO blood group) comprised the traits for which the observed spouse correlation reflected shared environmental effects. For all four traits the test statistics agreed with the known cause of spouse correlation; however, significance was not attained for height ratio or serum cholesterol. The ability to distinguish between the causes of spouse correlation in pedigree data presumably depends on trait and sample characteristics which remain to be delineated. Despite significant spouse correlation, its omission from the segregation analysis model did not undermine the inference of major locus inheritance for any of the four traits. However, the lack of an impact for these traits does not preclude an impact for other traits of ignoring the appropriate spouse correlation in segregation analysis.

Environment↗
PubMed1995

Segregation and linkage analysis of the complex trait Q1.

Segregation and linkage analysis of GAW9 Problem 2 quantitative trait 1 (Q1) was performed. Eight segregation models comprising all possible combinations of the environmental factor (EF), quantitative trait 2 (Q2), and quantitative trait 3 (Q3) as covariates were considered. Seven of the eight segregation models showed strong evidence for a major gene, the other model was marginal. When all genotypes are known, some evidence for linkage (lod > 2) was found to all three of the markers that affect Q1. Furthermore, four of the eight models each showed some linkage (lod > 2) to two of the three markers that affect Q1 with no false positives. Each of these segregation analysis major genes is a hybrid combination of the true multiple loci that affect Q1.

Alleles↗
PubMed2001

Stoppage: an issue for segregation analysis.

Segregation analysis assumes that the observed family-size distribution (FSD), i.e., distribution of number of offspring among nuclear families, is independent of the segregation ratio p. However, for certain serious diseases with early onset and diagnosis (e.g., autism), parents may change their original desired family size, based on having one or more affected children, thus violating that assumption. Here we investigate "stoppage," the situation in which such parents have fewer children than originally planned. Following Brookfield et al. [J Med Genet 25:181-185, 1988], we define a stoppage probability d that after the birth of an affected child, parents will stop having children and thus not reach their original desired family size. We first derive the full correct likelihood for a simple segregation analysis as a function of p, d, and the ascertainment probability pi. We show that p can be estimated from this likelihood if the FSD is known. Then, we show that under "random" ascertainment, the presence of stoppage does not bias estimates of p. However, for other ascertainment schemes, we show that is not the case. We use a simulation study to assess the magnitude of bias, and we demonstrate that ignoring the effect of stoppage can seriously bias the estimates of p when the FSD is ignored. In conclusion, stoppage, a realistic scenario for some complex diseases, can represent a serious and potentially intractable problem for segregation analysis.

Family Characteristics↗
PubMed1983

Hybrids between irradiated and unirradiated mammalian cells: survival and chromosome segregation.

We have studied the effect of X or gamma irradiation, of one parent of a cell hybrid, on hybrid viability and chromosome segregation. The hybrid types studied were mouse--Chinese hamster (which spontaneously lose a few hamster chromosomes) and Chinese hamster--human (which spontaneously lose most of the human complement). Preirradiation of the segregated and retained cell parent resulted in highly asymmetric hybrid survival curves; survival was greatly reduced when the retained parent was irradiated, especially for hamster-human fusions. Preirradiation of the parents of mouse-hamster hybrids modified both the direction and the extent of chromosome segregation, but no consistent effect on elimination was observed for hamster-human hybrids, and reversal of the direction of loss was never observed. These results are more consistent with the hypothesis that chromosome segregation from hybrids results from an intracellular chromosome selection, than with the hypothesis that cellular selection acts on randomly generated chromosome variants.

Animals↗
PubMed2006

Atom probe tomography characterization of solute segregation to dislocations.

The extent and level of solute segregation to individual dislocations may be quantified by atom probe tomography. The technique is best applied to materials with high dislocation densities, such as cold worked, mechanically alloyed, or neutron-irradiated materials. Dislocations may be observed in field ion images by a change of the normal concentric atom terraces at crystallographic poles to spirals. Solute segregation is evident in field ion images by brightly imaging atoms near the core of the dislocation. Dislocations are evident in atom maps in the three-dimensional atom probe by linear regions of enhanced solute concentration. The maximum separation envelope and tracer methods may be used to quantify the levels of solute at the dislocation at the subnanometer scale. Examples of interstitial and substitutional element segregation in a mechanically alloyed, oxide dispersion strengthened ferrite steel and phosphorus segregation to dislocations in neutron-irradiated pressure vessel steels are presented.

Electron Probe Microanalysis↗
PubMed1982

Genetic segregation in a high-yielding streptomycin-producing strain of Streptomyces griseus.

The streptomycin-producing Streptomyces griseus HP spontaneously segregated non-reverting derivatives with altered phenotypes. Clones characterized by increased spore formation and decreased streptomycin production were found. Two other types of derivatives were defective in aerial mycelium and streptomycin formation as well, but differed in the capacity to synthesize a yellow pigment. These derivatives were examined with respect to further properties. The stability of S. griseus HP was investigated in relation to conditions of continuous culture. Both at 26 and 30 degrees C, under glycerol and NH4Cl limitation a rapid segregation and enrichment of streptomycin-non-producing derivatives occurred. At 34 degrees C and glycerol limitation segregation began only after about 35 generations of continuous culture. In NH4Cl-limited chemostats the original strain was stable during 80 generations. In the course of the continuous culture experiments it was shown that the onset of genetic segregation within mycelia can be detected before it becomes obvious in colonies grown from the mycelia. This was achieved by fractionation of the mycelia by protoplast formation and subsequent plating on regeneration medium allowing colony growth and differentiation.

Ammonium Chloride↗
PubMed1994

Analysis of segregation in a human male reciprocal translocation carrier, t(1;11) (p36.3;q13.1), by two-colour fluorescence in situ hybridization.

Using centromeric probes specific for chromosomes 1 and 11, 13,071 sperm nuclei from a male reciprocal translocation heterozygote, 46,XY,t(1;11) (p36.3;q13.1), were analyzed by fluorescence in situ hybridization (FISH). Decondensed sperm nuclei were simultaneously hybridized with DNA probes for chromosome 1 (pUC177) and chromosome 11 (D11Z1). Results were as follows: 1/11 (82.45%), 1/1/- (3.45%), -/11/11 (4.85%), 1/1/11 (1.20%), 1/11/11 (1.14%), 1/- (4.33%), -/11 (2.50%), 1/1/11/11 (0.06%), 1/1/1/- (0.02%). Because both the normal chromosome and its translocated derivative carry the same centromeric sequences, FISH cannot differentiate between sperm resulting from alternate segregation and those produced by adjacent I segregation. Using the same donor, comparable segregation patterns were obtained from sperm chromosome karyotypes (Spriggs et al., 1992: Hum Genet 88:447-452) and from MII spermatocytes (Goldman and Hulten, 1993: Cytogenet Cell Genet 63:16-23), demonstrating that selection is not a factor in the human sperm/hamster oocyte fusion technique or during meiosis. Although FISH does not provide the detailed information afforded by sperm karyotyping, it is a valuable technique for studying segregation patterns in translocation heterozygotes.

Cell Nucleus↗
PubMed1998

Foraging behaviour and sexual segregation in bighorn sheep.

Like many sexually dimorphic ungulates, bighorn sheep, Ovis canadensis, form sexually segregated groups. Nursery groups include females, lambs and subadult males, while adult males form bachelor groups. Previous hypotheses to account for sexual segregation in ungulates have suggested sexual differences in energy requirements, predation risk and social preferences. I tested the hypothesis that differing nutritional demands, due to sexual dimorphism in body size, would lead to different movement patterns and time budgets. If ruminating/foraging schedules differed according to body size, males and females could not synchronize their activities and therefore would segregate by sex. To test this hypothesis, I observed a population of marked bighorns. I recorded the time males and females spent lying, grazing or walking during 8-14 h of focal-animal observations. Initial and final location of groups and steps taken per minute foraging were also noted. Females spent more time foraging and walking and had longer foraging and walking bouts than adult males, but did not differ in numbers of steps taken while foraging. Males spent more time lying than females. Subadult males switched between nursery and bachelor groups and changed their foraging behaviour depending on the type of group they were in. The distance moved was on average almost four times greater for female than for male groups. I suggest that sexual difference in time budgets and movement patterns make it difficult for males and females to stay in the same group and therefore lead to sexual segregation. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗