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PubMed1986

Segregation analysis of balanced pericentric inversions in pedigree data.

The results of the recent European collaborative prenatal study suggested a segregation distortion of balanced pericentric inversions from carrier fathers but not carrier mothers (Boué & Gallano 1984). In an attempt to confirm these unexpected results, we examined 216 pedigrees with balanced pericentric inversions collected from three centers and from the literature. We were unable to detect any significant deviation from the expected 1:1 segregation of balanced pericentric inversions to normal karyotypes among the offspring of either carrier parent. To clarify the discrepancy between the studies, we reanalyzed the data from the prenatal study using all karyotyped individuals and, assuming conventional ascertainment rules, found a normal segregation pattern. We conclude that balanced pericentric inversions segregate normally in both males and females and that some retrospectively selected pedigrees were included as prospective in the prenatal study and this misclassification caused the apparent segregation distortion from carrier fathers.

Chromosome Inversion↗
PubMed1982

Genetic studies of insulin-dependent diabetes mellitus: segregation and linkage analyses.

The inclusion of HLA data in genetic studies of insulin-dependent diabetes mellitus (IDDM) has not led to conclusive segregation models for IDDM so far. As a new approach, we first applied complex segregation analysis, independently of HLA data, to two combined Danish family materials. Then the best fitting segregation model was entered into linkage analysis of a third material, including family as well as HLA data. The best solution obtained in the segregation analysis was a mixed model, including an intermediate gene, which on the penetrance scale acts as a recessive, together with a polygenic component. The linkage analysis showed an overall recombination fraction of 0.0417 with high coupling frequencies for the HLA-DR3 and HLA-DR4 alleles and the putative disease susceptibility gene. However, when the pedigrees were divided according to whether or not the proband had the heterozygous HLA-phenotype DR3/DR4, a maximum likelihood ratio test for heterogeneity was significant, with estimated recombination fractions of 0.0 and 0.0963 in HLA-DR3/DR4 pedigrees and the remaining pedigrees, respectively. In total, we found convincing evidence that two familial factors contribute to IDDM: a locus within HLA, which very well may be DR; and an unlinked mechanism which is unimportant for HLA-DR3/DR4 but simulates recombination. If confirmed, this conclusion has important implications for further genetic studies of IDDM and complex segregation analyses of family materials sampled according to criteria which include HLA data of the probands are highly needed.

Adolescent↗
PubMed1981

Segregation of specific classes of messenger RNA into free and membrane-bound polysomes.

Analysis of mRNA populations from rat liver rough microsomes and free polysomes by homologous and heterologous cDNA . mRNA hybridization shows that the two mRNA populations are distinct, demonstrating that specific mRNA classes are efficiently segregated for translation in association with endoplasmic reticulum membranes. We estimate that approximately 90% of the mRNA in membrane-bound polysomes contains a diverse set of messengers with a minimum of 500--2000 different species although approximately 5--8 messengers may constitute 25--30% of the mRNA mass. The complexity of the mRNA population of free polysomes appears to be comparable to that estimated for total liver poly(A) + mRNA by other investigators, and is likely to be substantially greater than that of the bulk of bound mRNA. In addition, mRNA in free polysomes lacks the high abundance class characteristic of mRNA-bound polysomes. The substantial complexity of the bound mRNA population suggests that the segregation of polysomes in rough microsomes is not limited to a small class specialized in manufacturing secretory proteins, but extends to polysomes engaged in the synthesis of proteins for intracellular distribution. The segregation of specific messengers into the free and membrane-bound classes was abolished when polysome disassembly was induced by administration of ethionine. Thus, messenger RNA molecules themselves lacked the capacity for segregation, although they contain information for segregation which is expressed during translation. These findings are consistent with the presence of signal sequences in nascent polypeptides which determine the attachment of ribosomes to endoplasmic reticulum membranes.

Animals↗
PubMed2005

Birth-date-dependent segregation of the mouse cerebral cortical neurons in reaggregation cultures.

Cerebral cortical neurons form a six-layered structure in which their position depends on their birth date. This developmental process requires the presence of Reelin, which is secreted by Cajal-Retzius cells in the cortical marginal zone (MZ). However, it is still unclear whether the migration from the ventricular zone (VZ) to beneath the MZ is essential for the neurons to segregate into layers. Previous transplantation studies of ferret cerebral cortical neurons suggested that their ultimate laminar fate is, at least to some extent, determined in the VZ but it is unknown how 'laminar fate' eventually positions cells in a specific layer. To explore the segregation properties of mouse cortical cells that have not yet arrived beneath the MZ, embryonic day (E)16 VZ and intermediate zone (IMZ) cells were dissociated and allowed to reaggregate for 1-4 days in vitro. The results suggested that the migrating neurons in the IMZ at E16 preferentially located near the centre of the aggregates, more than did the proliferative cells from the VZ. The birth-date labelling followed by the dissociation-reaggregation culture suggested that the segregation properties of the E16 IMZ was characteristic of the E14-born cells, which were migrating in the IMZ at E16, but they were not general properties of migrating IMZ cells. This birth-date-dependent segregation mechanism was also observed in the Reelin signalling-deficient yotari cells. These findings suggest that cortical neurons acquire a birth-date-dependent segregation mechanism before their somas reach the MZ.

Age Factors↗
PubMed2006

Pitch-based monaural segregation of reverberant speech.

In everyday listening, both background noise and reverberation degrade the speech signal. Psychoacoustic evidence suggests that human speech perception under reverberant conditions relies mostly on monaural processing. While speech segregation based on periodicity has achieved considerable progress in handling additive noise, little research in monaural segregation has been devoted to reverberant scenarios. Reverberation smears the harmonic structure of speech signals, and our evaluations using a pitch-based segregation algorithm show that an increase in the room reverberation time causes degraded performance due to weakened periodicity in the target signal. We propose a two-stage monaural separation system that combines the inverse filtering of the room impulse response corresponding to target location and a pitch-based speech segregation method. As a result of the first stage, the harmonicity of a signal arriving from target direction is partially restored while signals arriving from other directions are further smeared, and this leads to improved segregation. A systematic evaluation of the system shows that the proposed system results in considerable signal-to-noise ratio gains across different conditions. Potential applications of this system include robust automatic speech recognition and hearing aid design.

Algorithms↗
PubMed1997

Perceptual segregation of a harmonic from a vowel by interaural time difference and frequency proximity.

The five experiments reported here examine the conditions under which sounds differing in their interaural time difference (ITD) are segregated for the purposes of perceiving a vowel's identity. Experiment 1 confirms previous findings that (i) a difference in ITD provides only a very weak cue for segregating a vowel's 500-Hz harmonic from the remainder of an isolated vowel; (ii) embedding the harmonic in a series of 500-Hz tones produces some segregation, which is enhanced if the harmonic and the tones differ in ITD from the rest of the vowel; and (iii) when these latter sounds are presented in the same block as isolated vowels, they facilitate segregation of the harmonic by ITD in the isolated vowels. The subsequent experiments show that this last effect, across-trial facilitation, is only produced by sounds which cue both the frequency and the ITD of the harmonic; either alone is insufficient. We also show that: (i) a single cue tone at the frequency of the harmonic is sufficient to facilitate the use of ITD in grouping; (ii) sequential organization by frequency proximity dominates over sequential organization by ITD when simultaneous sound sources are present; and (iii) the effectiveness of a cue tone can be abolished by capturing it into a synchronous harmonic complex. The experiments clarify the conditions under which ITDs contribute to the segregation of simultaneous sounds.

Auditory Threshold↗
PubMed1999

The role of spectral and periodicity cues in auditory stream segregation, measured using a temporal discrimination task.

In a previous paper, it was shown that sequential stream segregation could be based on both spectral information and periodicity information, if listeners were encouraged to hear segregation [Vliegen and Oxenham, J. Acoust. Soc. Am. 105, 339-346 (1999)]. The present paper investigates whether segregation based on periodicity information alone also occurs when the task requires integration. This addresses the question: Is segregation based on periodicity automatic and obligatory? A temporal discrimination task was used, as there is evidence that it is difficult to compare the timing of auditory events that are perceived as being in different perceptual streams. An ABA ABA ABA... sequence was used, in which tone B could be either exactly at the temporal midpoint between two successive tones A or slightly delayed. The tones A and B were of three types: (1) both pure tones; (2) both complex tones filtered through a fixed passband so as to contain only harmonics higher than the 10th, thereby eliminating detectable spectral differences, where only the fundamental frequency (f0) was varied between tones A and B; and (3) both complex tones with the same f0, but where the center frequency of the spectral passband varied between tones. Tone A had a fixed frequency of 300 Hz (when A and B were pure tones) or a fundamental frequency (f0) of 100 Hz (when A and B were complex tones). Five different intervals, ranging from 1 to 18 semitones, were used. The results for all three conditions showed that shift thresholds increased with increasing interval between tones A and B, but the effect was largest for the conditions where A and B differed in spectrum (i.e., the pure-tone and the variable-center-frequency conditions). The results suggest that spectral information is dominant in inducing (involuntary) segregation, but periodicity information can also play a role.

Adolescent↗
PubMed1988

Prenatal tetrodotoxin infusion blocks segregation of retinogeniculate afferents.

In the adult mammalian visual system, ganglion cell axons from the two eyes are segregated from each other into separate layers within their principal target, the lateral geniculate nucleus. The involvement of spontaneously generated action potential activity in the process of segregation was investigated during the fetal period in which segregation normally occurs in the cat, between embryonic day 45 (E45) and birth (E65). Tetrodotoxin, which blocks the voltage-sensitive sodium channel, was used to prevent action potentials. Fetuses received continuous intracranial infusions of tetrodotoxin from osmotic minipumps implanted in utero on E42. After a 2-week infusion, intraocular injections of anterograde tracers revealed that tetrodotoxin prevented segregation. The contralateral projection filled the lateral geniculate nucleus uniformly, and the ipsilateral projection expanded to occupy most of what would normally be contralaterally innervated layer A. Thus, in the fetus, long before the onset of vision, spontaneous action potential activity is likely to be present in the visual system and to contribute to the segregation of the retinogeniculate pathway.

Afferent Pathways↗
PubMed1977

Medium-dependent variation of deoxyribonucleic acid segregation in Escherichia coli.

The degree to which deoxyribonucleic acid segregates nonrandomly has been investigated for Escherichia coli B/r growing in different media. The degree of nonrandom segregation observed is dependent on the medium, with segregation becoming less random as the growth rate decreases. This indicates that there must be some varying probabilistic component to the segregation process. A probabilistic modification of the Pierucci-Zuchowski model is proposed as well as a probabilistic model, in which it is proposed that deoxyribonucleic acid strands segregate, with a probability greater than 0.5, in the same direction (toward the same pole) as at the previous cell division.

Cell Division↗
PubMed1982

Conformation and segregation of nucleoids accompanying cell length extension after completion of a single round of DNA replication in germinated and outgrowing Bacillus subtilis spores.

When germinating spores of the temperature-sensitive DNA initiation mutant of Bacillus subtilis TsB134 are shifted to the restrictive temperature at a time such that just one or two rounds of replication are accomplished, the completed, nonreplicating nucleoids that form eventually adopt a doublet conformation. This conformation has now been observed after fixation by glutaraldehyde or osmium tetroxide, as well as by Formalin as found previously. The doublet was observed in media of different degrees of richness and under both light and electron microscopes. Electron micrographs of serial sections through the doublet were consistent with its formation by the gradual pulling apart of a single mass of DNA into two lobes. A systematic study was made of the effect of the time of shifting from the permissive to the restrictive temperature and of the restrictive temperature used on the number of nucleoids segregating within the outgrowing rod. It was established that the doublet nucleoid behaved as a single unit in replication control and segregation in both rich and poor media. Measurement of the relative position of the two segregating nucleoids within the outgrowing rod after completion of just one round of replication yielded quantitative information on the segregation and cell length extension processes. Segregation was accompanied by cell length extension at approximately equal rates on both sides of each nucleoid. Furthermore, the data were consistent with an exponential increase in such an extension with time over the early and major portion of the period studied, but it was not possible to rule out other models of length extension.

Bacillus subtilis↗
PubMed1963

SMALL-CELL SEGREGANTS FROM A POSSIBLY HOMOZYGOUS DIPLOID STRAIN OF ESCHERICHIA COLI.

Ogg, James E. (Colorado State University, Fort Collins) and Ronald D. Humphrey. Small-cell segregants from a possibly homozygous diploid strain of Escherichia coli. J. Bacteriol. 85:801-807. 1963.-Evidence was presented to show that a homozygous possibly diploid strain of Escherichia coli, when grown in a chemically defined medium under the conditions described in this report, will yield small-cell segregants that have haploid characteristics. The segregants have one-half as much deoxyribonucleic acid per cell as the diploid, give exponential survival curves when exposed to X rays, and have fermentative characteristics similar to the original haploid parent strain of the homozygous diploid strain. No detectable changes in surface antigens were associated with the segregation phenomenon. The haploidlike segregants can be converted to the diploid radiation-resistant state by growing them in the presence of camphor vapors.

Colorado↗
PubMed1993

A DNA polymerase mutation that suppresses the segregation bias of an ARS plasmid in Saccharomyces cerevisiae.

Yeast autonomously replicating sequence (ARS) plasmids exhibit an unusual segregation pattern during mitosis. While the nucleus divides equally into mother and daughter cells, all copies of the ARS plasmid will often remain in the mother cell. A screen was designed to isolate mutations that suppress this segregation bias. A plasmid with a weak ARS (wARS) that displayed an extremely high segregation bias was constructed. When cells were grown under selection for the wARS plasmid, the resulting colonies grew slowly and had abnormal morphology. A spontaneous recessive mutation that restored normal colony morphology was identified. This mutation suppressed plasmid segregation bias, as indicated by the increased stability of the wARS plasmid in the mutant cells even though the plasmid was present at a lower copy number. An ARS1 plasmid was also more stable in mutant cells than in wild-type cells. The wild-type allele for this mutant gene was cloned and identified as POL delta (CDC2). This gene encodes DNA polymerase delta, which is essential for DNA replication. These results indicate that DNA polymerase delta plays some role in causing the segregation bias of ARS plasmids.

Alleles↗
PubMed1983

Evaluation of segregation ratio in Wilson's disease.

Two problems relating to segregation analysis for Wilson's disease are discussed and a practical solution is presented. A problem in the ascertainment of families with Wilson's disease is illustrated by comparing segregation ratios calculated by the single selection, complete truncate, and multiple incomplete selection methods. The effect on the segregation ratio of exclusion from the analysis of those sibs who had died of other diseases at a young age is also discussed and a method of adjustment of the number of the affected using the data on age at onset is proposed. The segregation ratio by multiple incomplete selection (Weinberg proband method) after adjustment for those sibs who had died of other diseases was 0.243, consistent with the theoretical value for autosomal recessive inheritance. The segregation ratio calculated by the single selection method tended to give a lower value, while that calculated by the complete truncate method was greater than the theoretical value. Recessive inheritance is, however, supported. The actual effect of exclusion of those sibs who had died of other diseases on gene frequency estimation is shown to be very small.

Gene Frequency↗
PubMed1995

Three-to-one segregation from reciprocal translocation quadrivalents in Neurospora and its bearing on the interpretation of spore-abortion patterns in unordered asci.

In Neurospora, viable ascospores become black (B) when mature, whereas ascospores that are deficient for a chromosome segment are inviable and usually fail to blacken. The presence of a chromosome rearrangement can be recognized and the type of rearrangement can usually be inferred by visual inspection of asci. When a cross is heterozygous for a reciprocal translocation, asci with eight black ascospores (8B:0W) and asci with eight abortive unpigmented ("white" (W)) ascospores (0B:8W) are theoretically produced in equal numbers if homologous centromeres are equally likely to segregate from the quadrivalent in alternate or adjacent modes. In addition, 4B:4W asci are produced with a frequency characteristic of each reciprocal translocation. Information on ascospore-abortion patterns in Neurospora crassa has come predominantly from unordered ascospore octads ejected from the perithecium. Unordered asci of the 4B:4W type were initially presumed to originate by interstitial crossing over in a centromere-breakpoint interval and their frequency was used as a predictor of centromere locations. However, 4B:4W asci can result not only from interstitial crossing over but also from nondisjunction of centromeres at the first meiotic division, which leads to 3:1 segregation. Ordered linear 4B:4W asci retain the sequence information necessary for distinguishing one mode of origin from the other but unordered asci do not. Crossing over results in one abortive duplication-deficiency ascospore pair in each opposite half of a linear ascus, while 3:1 segregation places both abortive ascospore pairs together, either in the distal half or the basal half of the ascus. In the present study, perithecia were opened and intact linear asci were examined in crosses heterozygous for a varied sample of translocations. Three-to-one segregation rather than interstitial crossing over is apparently the main cause of 4B:4W asci when breakpoints are near centromeres, whereas crossing over is responsible for most or all 4B:4W asci when breakpoints are far-distal. Three-to-one segregation does not impair the usefulness of ejected unordered asci for detecting chromosome rearrangements. Ejected octads are superior to ordered linear asci for distinguishing one type of rearrangement from another, because ascus ejection from the perithecium does not occur until viable ascospores are fully pigmented, enabling true 0B:8W asci to be distinguished from those with eight immature ascospores.

Centromere↗
PubMed2005

Weak segregation theory and non-conventional morphologies in the ternary ABC triblock copolymers.

The statistical theory of microphase separation in the ternary ABC triblock copolymers is presented and the corresponding phase diagrams are built both for the linear and miktoarm copolymers. For this purpose the Leibler weak segregation theory in molten diblock copolymers is generalized to multi-component monodisperse block copolymers with due regard for the 2nd shell harmonics contributions defined in the paper. The Hildebrand approximation for the chi-parameters is used. The physical meaning of this and alternative choices for the chi-parameters is discussed. The symmetric A(f)B(1-2f)C(f) copolymers with the middle block non-selective with respect to the side ones are shown to undergo the continuous ODT not only into the lamellar phase but also, instead, into various non-conventional cubic phases (depending on the middle block composition it could be the simple cubic, face-centered cubic or non-centrosymmetric phase, which reveals the symmetry of I4(1) 32 space group No. 214 first predicted to appear in molten block copolymers). For asymmetric linear ABC copolymers a region of compositions is found where the weakly segregated gyroid (double gyroid) phase exists between the planar hexagonal and lamellar or one of the non-conventional cubic phases up to the very critical point. In contrast, the miktoarm (star) ABC block copolymers with one of its arm non-selective with respect to the two others are shown to reveal a pronounced tendency towards strong segregation, which is preceded by increase of stability of the conventional BCC phase and a peculiar weakly segregated BCC phase (BCC(3)), where the dominant harmonics belong to the 3rd coordination sphere of the reciprocal lattice. The validity region of the developed theory is discussed and outlined in the composition triangles both for linear and miktoarm copolymers. We present also the list of the 2nd shell harmonics (SAXS reflections) allowed and prohibited in some of the non-conventional morphologies due to the weak segregation considerations and comparison of our results with the preceding SCFT treatment of the ABC copolymers by Matsen.

Journal Article↗
PubMed1998

Sperm segregation analysis of a complex chromosome rearrangement, 2;22;11, by whole chromosome painting.

Using the human sperm-hamster oocyte fusion technique and whole chromosome painting, we studied sperm chromosome segregation in a male heterozygous for a complex chromosome rearrangement, 46,XY,-2, +der(2)t(2;11)(q13; q23),-11,+der(11)t(11;22)(q23;q11.2),-22, +der(22)t(2;22)(q13; q11.2). A total of 208 sperm complements were analyzed. The frequency of sperm carrying a normal or a balanced complement was 13.5% (9.62% and 3.85%, respectively). The frequency of unbalanced sperm was 86.5% (64.9% from 3:3 segregation, including 30 different types; 20.7% from 4:2 segregation, including 21 different types; and 0.96% from 5:1 segregation, including 2 different types). The sex ratio, determined in 134 sperm complements, did not differ from the expected 1:1 ratio. The results obtained in this study are compatible with the formation, during the synaptic process, of a complex hexavalent figure involving chromosomes 2, 11, and 22. The behavior and segregation of this complex figure would explain the high frequency (86.5%) of unbalanced complements observed in this carrier.

Animals↗
PubMed2005

Auditory stream segregation in the songbird forebrain: effects of time intervals on responses to interleaved tone sequences.

For both humans and other animals, the abilities to integrate separate sound elements over time into coherent perceptual representations, or 'auditory streams', and to segregate these auditory streams from other interleaved sounds are critical for hearing and vocal communication. In humans and European starlings (Sturnus vulgaris) the ability to perceptually segregate a simple interleaved tone sequence comprised of two alternating tones differing in frequency (ABA-ABA-ABA-...) into separate auditory streams of A and B tones is promoted at larger frequency separations (DeltaF) between the A and B tones. In humans, segregating A and B tones into different streams also appears to be promoted at shorter interstimulus intervals (ISI) between tones within a stream (e.g., between consecutive A tones). Here, we used the ABA experimental paradigm to investigate the influence of different time intervals between A and B tones in repeated ABA triplets on neural responses in the starling forebrain. The main finding from the study is that a DeltaF-dependent effect of ISI had a large influence on the relative responses to A and B tones. Responses to B tones were suppressed, relative to A-tone responses, when the A and B tones were more similar in frequency (smaller DeltaFs) and occurred at shorter ISIs. We attribute these suppressive effects to physiological forward masking and suggest that forward masking functions as a mechanism for segregating neural responses to interleaved tones in tonotopic space. We discuss the relevance of our physiological data with respect to previous electrophysiological studies of auditory stream segregation in mammals and previous perceptual studies in humans.

Animals↗
PubMed1995

Meiotic segregation in males heterozygote for reciprocal translocations: analysis of sperm nuclei by two and three colour fluorescence in situ hybridization.

The meiotic segregation of chromosomes was analysed in three reciprocal translocation carriers, using FISH on interphase spermatozoa. The segregation pattern was first studied in 27,844 spermatozoa from two siblings carrying the reciprocal translocation t(6;11)(q14;p14). Three centromeric probes, specific for chromosomes 6, 11 and 1, were simultaneously hybridized so that all centric fragments as well as the ploidy of each cell could be determined by three colour FISH. For both subjects, the respective frequencies of alternate/adjacent 1, adjacent 2, 3:1 and 4:0 segregation modes were 88%, 9%, 3+ and < 1%. In another reciprocal translocation t(2;14)(p23.1;q31), a two colour FISH analysis was performed on 4,610 spermatozoa, using a chromosome 2 centromeric probe and a YAC probe located on the centric fragment of chromosome 14. Frequencies of alternate/adjacent 1, adjacent 2, and 3:1 segregations were 89%, 5.2%, and 5.8% respectively. The segregation of chromosomes X, Y and 1 were also analyzed with three colour FISH on the spermatozoa from all three translocation carriers, in order to detect an interchromosomal effect. Aneuploidy rates for the X and Y chromosomes were found to be in the same range in the three translocation carriers and control donors, but disomy 1 rates were slightly increased in the translocation carriers.

Cell Nucleus↗