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PubMed2001

Segregation of hematuria in thin basement membrane disease with haplotypes at the loci for Alport syndrome.

BACKGROUND: Inherited hematuria is common and is usually attributed to thin basement membrane disease (TBMD). The aim of this study was to determine how often hematuria in families with TBMD segregated with haplotypes at the chromosomal loci for autosomal recessive and X-linked Alport syndrome (COL4A3/COL4A4 and COL4A5, respectively). METHODS: The families of 22 individuals with TBMD on renal biopsy and with urinary glomerular red blood cell (RBC) counts of more than 50,000/mL were studied using phase-contrast microscopy of the urine and DNA microsatellite markers. Eighteen families had at least two members with hematuria. RESULTS: Hematuria segregated with or was consistent with segregation at the COL4A3/COL4A4 locus in eight (36%) families (P < 0.05 in 5 of these) and at the COL4A5 locus in four (18%) families (P < 0.05 in 2). The lack of segregation in the other 10 (45%) families may have occurred because of incomplete penetrance of the hematuria, de novo mutations, coincidental hematuria in other family members, or the presence of a novel gene locus. In four different families, three of which had hematuria that segregated with the COL4A3/COL4A4 locus, four family members with the hematuria haplotype had spouses with coincidental hematuria (4 of 29, 14%). However, none of their four offspring who had also inherited the hematuria haplotype had the clinical features of autosomal recessive Alport syndrome. CONCLUSIONS: Hematuria in families with TBMD commonly segregates with the COL4A3/COL4A4 locus and thus results from mutations in the same genes as autosomal recessive Alport syndrome. Sometimes TBMD may be confused with the carrier state for X-linked Alport syndrome. However, nearly half of the families in this study had hematuria that did not segregate with the loci for either autosomal recessive or X-linked Alport syndrome.

Adolescent↗

PubMed2005

Colour, polarity, disparity, and texture contributions to motion segregation.

We measured how different cues are combined in motion-segregation processes by using motion stimuli where randomly distributed target dots were organised in global revolving motion while the remaining noise dots performed random motion. Target dots were cued with a different colour, polarity, disparity depth, or texture orientation than the noise dots, or they were the same as the noise dots. The stimuli were presented with a prolonged static cue preview which provided position cues to target dots or, briefly with static pre-target and post-target noise frames, which provided false position cues (no preview). All cues efficiently facilitated global motion segregation in cued-preview conditions. Colour completely failed to facilitate global motion segregation in no-preview conditions. Polarity and disparity facilitated segregation in no-preview conditions, although sensitivities were lower than in the preview conditions. Remarkably, texture orientation largely facilitated motion segregation by the same amount in both cued-preview and no-preview conditions. So, colour provides only position cues to the motion-segregation task whereas texture orientation, disparity, and to a lesser extent polarity are integrated with the segregation process.

Color Perception↗

PubMed2001

Gender segregation in childhood: a test of the interaction style theory.

The authors investigated the play/interaction-style theory of gender segregation with a sample of 39 children aged 2 to 5 years (primarily Caucasian). According to this theory, children prefer playmates with styles of play or interaction that are similar to their own. Because such styles are sex differentiated, same-sex playmate preference (i.e., gender segregation) results. The authors observed children during free play to determine preferred playmates and gender segregation level, and they used teacher ratings to derive play/interaction-style scores. The authors used a multiple regression approach to path analysis to analyze effects of sex of participant, participants' play/interaction-style scores, playmates' play/interaction-style scores, and degree of gender segregation to determine their effects on one another. The authors observed significant levels of gender segregation, with highly aggressive or active children displaying less segregation than their peers did. However, gender segregation was not associated with a preference for playmates with similar play or interaction styles.

Child↗

PubMed1997

Detection of gene-environment interactions in joint segregation and linkage analysis.

We compare approaches for analysis of gene-environment (G x E) interaction, using segregation and joint segregation and linkage analyses of a quantitative trait. Analyses of triglyceride levels in a single large pedigree demonstrate the two methods and show evidence for a significant interaction (P=.015 when segregation analysis is used; P=.006 when joint analysis is used) between a codominant major gene and body-mass index. Genotype-specific correlation coefficients, between triglyceride levels and body-mass index, estimated from the joint model are rAA=.72, rAa=.49, and raa=. 20. Several simulation studies indicate that joint segregation and linkage analysis leads to less-biased and more-efficient estimates of a G x E-interaction effect, compared with segregation analysis alone. Depending on the heterozygosity of the marker locus and its proximity to the trait locus, we found joint analysis to be as much as 70% more efficient than segregation analysis, for estimation of a G x E-interaction effect. Over a variety of parameter combinations, joint analysis also led to moderate (5%-10%) increases in power to detect the interaction. On the basis of these results, we suggest the use of combined segregation and linkage analysis for improved estimation of G x E-interaction effects when the underlying trait gene is unmeasured.

Body Mass Index↗

PubMed2000

Meiotic segregation analysis of RB1 alleles in retinoblastoma pedigrees by use of single-sperm typing.

In hereditary retinoblastoma, different epidemiological studies have indicated a preferential paternal transmission of mutant retinoblastoma alleles to offspring, suggesting the occurrence of a meiotic drive. To investigate this mechanism, we analyzed sperm samples from six individuals from five unrelated families affected with hereditary retinoblastoma. Single-sperm typing techniques were performed for each sample by study of two informative short tandem repeats located either in or close to the retinoblastoma gene (RB1). The segregation probability of mutant RB1 alleles in sperm samples was assessed by use of the SPERMSEG program, which includes experimental parameters, recombination fractions between the markers, and segregation parameters. A total of 2,952 single sperm from the six donors were analyzed. We detected a significant segregation distortion in the data as a whole (P=.0099) and a significant heterogeneity in the segregation rate across donors (.0092). Further analysis shows that this result can be explained by segregation distortion in favor of the normal allele in one donor only and that it does not provide evidence of a significant segregation distortion in the other donors. The segregation distortion favoring the mutant RB1 allele does not seem to occur during spermatogenesis, and, thus, meiotic drive may result either from various mechanisms, including a fertilization advantage or a better mobility in sperm bearing a mutant RB1 gene, or from the existence of a defectively imprinted gene located on the human X chromosome.

Adult↗

PubMed1993

QTL analysis of transgressive segregation in an interspecific tomato cross.

Two accessions, representing the species Lycopersicon esculentum (cultivated tomato) and Lycopersicon pennellii (a wild relative), were evaluated for 11 quantitative traits and found to be significantly different for 10 of the traits. Transgressive segregation was observed for eight of the traits in a large interspecific F2 population. When restriction fragment length polymorphism markers were used as probes for the quantitative trait loci (QTL) underlying the traits, 74 significant QTL (LOD > 2) were detected. Thirty-six percent of those QTL had alleles with effects opposite to those predicted by the parental phenotypes. These QTL were directly related to the appearance of transgressive individuals in the F2 for those traits which showed transgressive segregation. However, the same types of QTL (with allelic effects opposite to those predicted by the parents) were also observed for traits that did not display transgressive segregation in the F2. One such trait was dry weight accumulation. When two overdominant QTL (detected in the F2) for this trait were backcrossed into the L. esculentum genetic background, transgressive individuals were recovered and their occurrence was associated with the two QTL demonstrating the potential for transgressive segregation for all characters and implicating overdominance as a second cause of transgressive segregation. Epistasis was not implicated in transgressive segregation in either the F2 or backcross generations. Results from this research not only reveal the basis of wide-cross transgressive segregation, but demonstrate that molecular markers can be used to identify QTL (from wild species) responsible for transgressive phenotypes and to selectively transfer them into crop species. This strategy might be used to improve many traits of economic importance including those for which wild species appear phenotypically inferior to their cultivated counterparts.

Alleles↗

PubMed1999

The role of centromere alignment in meiosis I segregation of homologous chromosomes in Saccharomyces cerevisiae.

During meiosis, homologous chromosomes pair and then segregate from each other at the first meiotic division. Homologous centromeres appear to be aligned when chromosomes are paired. The role of centromere alignment in meiotic chromosome segregation was investigated in Saccharomyces cerevisiae diploids that contained one intact copy of chromosome I and one copy bisected into two functional centromere-containing fragments. The centromere on one fragment was aligned with the centromere on the intact chromosome while the centromere on the other fragment was either aligned or misaligned. Fragments containing aligned centromeres segregated efficiently from the intact chromosome, while fragments containing misaligned centromeres segregated much less efficiently from the intact chromosome. Less efficient segregation was correlated with crossing over in the region between the misaligned centromeres. Models that suggest that these crossovers impede proper segregation by preventing either a segregation-promoting chromosome alignment on the meiotic spindle or some physical interaction between homologous centromeres are proposed.

Centromere↗

PubMed2003

Nonrandom homolog segregation at meiosis I in Schizosaccharomyces pombe mutants lacking recombination.

Physical connection between homologous chromosomes is normally required for their proper segregation to opposite poles at the first meiotic division (MI). This connection is generally provided by the combination of reciprocal recombination and sister-chromatid cohesion. In the absence of meiotic recombination, homologs are predicted to segregate randomly at MI. Here we demonstrate that in rec12 mutants of the fission yeast Schizosaccharomyces pombe, which are devoid of meiosis-induced recombination, homologs segregate to opposite poles at MI 63% of the time. Residual, Rec12-independent recombination appears insufficient to account for the observed nonrandom homolog segregation. Dyad asci are frequently produced by rec12 mutants. More than half of these dyad asci contain two viable homozygous-diploid spores, the products of a single reductional division. This set of phenotypes is shared by other S. pombe mutants that lack meiotic recombination, suggesting that nonrandom MI segregation and dyad formation are a general feature of meiosis in the absence of recombination and are not peculiar to rec12 mutants. Rec8, a meiosis-specific sister-chromatid cohesin, is required for the segregation phenotypes displayed by rec12 mutants. We propose that S. pombe possesses a system independent of recombination that promotes homolog segregation and discuss possible mechanisms.

Base Sequence↗

PubMedDate not supplied

Segregation distortion for seed testa color in Mungbean (Vigna radiata L. Wilcek).

Genetic segregation experiments with plant species are commonly used for understanding the inheritance of traits. A basic assumption in these experiments is that each gamete developed from megasporogenesis has an equal chance of fusing with a gamete developed from microsporogenesis, and every zygote formed has an equal chance of survival. If gametic and/or zygotic selection occurs whereby certain gametes or zygotic combinations have a reduced chance of survival, progeny distributions are skewed and are said to exhibit segregation distortion. In this study, inheritance data are presented for the trait seed testa color segregating in large populations (more than 200 individuals) derived from closely related mungbean (Vigna radiata L. Wilcek) taxa. Segregation ratios suggested complex inheritance, including dominant and recessive epistasis. However, this genetic model was rejected in favor of a single-gene model based on evidence of segregation distortion provided by molecular marker data. The segregation distortion occurred after each generation of self-pollination from F1 thru F7 resulting in F7 phenotypic frequencies of 151:56 instead of the expected 103.5:103.5. This study highlights the value of molecular markers for understanding the inheritance of a simply inherited trait influenced by segregation distortion.

Color↗

PubMed2000

Reverse and intermediate segregation of large beads in dry granular media

Mixtures of two types of glass beads have been sheared in a chute flow, in a half-filled rotating drum, and placed in a funnel to form a pile. In the three experimental devices, for small size ratios, there is a segregation of the large beads at the surface of the flowing phase (usual case), but for high size ratios (above about 5) the large beads segregate inside (reverse segregation). Precise measurements show that the segregation drives the large beads to an intermediate level inside the bed. In all devices, there is a continuous evolution of the location of the segregated beads from the surface to deep inside, when increasing the size ratio between the beads. The location of the segregated beads at intermediate levels is well defined both for high size ratios (above 5) and for very small size ratios (about 2), the level being very close to the surface in that case. The reverse and intermediate segregations are masked when using high fractions of large beads in the experiments. Their interpretation involves the high mass of the large particles balancing geometrical effects at a particular intermediate level inside the flowing layer.

Journal Article↗

PubMed1978

Probabilistic behavior of DNA segregation in Escherichia coli.

The pattern of segregation of DNA in Escherichia coli B/rK was analyzed by using the Methocel technique for forming chains of cells and the membrane binding elution method. Strain B/rK was shown to have a relatively high degree of nonrandom segregation and was used in a critical experiment to test the proposal that only one DNA strand acts nonrandomly during segregation. Thymidine-labeled cells were bound to a nitrocellulose membrane, and newly dividing cells were eluted from the membrane for six generations. The segregation of DNA in the eluted cells as well as in the cells bound to the membrane was examined by the Methocel technique. No difference in segregation was found between the two populations of cells, a result which indicates that the two strands are equivalent in segregation and that the pattern of segregation is not the result of a permanent binding of any strand to a pole of a cell.

Cell Division↗

PubMed1987

Levels of fos, ets2, and myb proto-oncogene RNAs correlate with segregation of chromosome 11 of normal cells and with suppression of tumorigenicity in human cell hybrids.

The tumorigenicity in nude mice of human carcinoma-derived D98AH2 (D98) cells is suppressed when cell hybrids are made by fusing these cells with normal human diploid cells. Selection for hybrids that have segregated chromosomes results in the recovery of tumorigenic segregants. These segregants have all lost at least one copy of chromosome 11 of the diploid cell parent. Earlier we found that the parental D98 cells had detectable levels of mRNA specific for 13 of 21 proto-oncogenes examined. To determine if transregulation of proto-oncogenes by genes of the normal cell occurs in such hybrids, the steady-state levels of mRNA specific to 22 proto-oncogenes in the parental cells were compared with those of nontumorigenic D98 X human diploid hybrids as well as with those of their tumorigenic segregants and with the cells of the resulting tumors. The only chromosome consistently segregated in the latter was chromosome 11 of the diploid cell. fos and ets2 RNA levels and the amount of fos protein were consistently elevated in the segregants compared with amounts in the original hybrids. An unexpected finding was the inverse relationship for myb RNA that was barely detected in the parental D98 cells but was at least 10-fold elevated in hybrids that did not have segregated chromosomes compared with those that did. These patterns were evident in RNAs prepared from both subconfluent and confluent cell cultures. The findings suggest that genes of the normal cell parent can affect proto-oncogene expression. Whether the genes affecting fos, ets2, and myb RNA levels are on chromosome 11 and whether these alterations are causally related to the tumorigenic phenotype of the hybrid remain to be determined.

Animals↗

PubMed1986

Chromosome segregation from cell hybrids. II. Do differences in parental cell growth rates and phase times determine direction of loss?

The hypothesis that the direction of chromosome segregation in cell hybrids is determined by the interaction of parent cell cycles, or S-phase times, predicts that the segregant parent will always be the one with the longer cycle, or the longer S phase, and that late replicating chromosomes will be more frequently lost. We have tested this hypothesis by studying cell cycle parameters of mouse, Chinese hamster, and platypus parent cells and by observing chromosome loss and replication patterns in hybrids between them. Two types of hybrids have been studied: mouse-hamster hybrids showed gradual segregation, in one or other direction, of 10-60% chromosomes, while rodent-platypus hybrids (which could be selected under conditions optimal for either parent cell) showed rapid and extreme segregation of platypus chromosomes. We found no correlation between the direction of segregation and the relative lengths of parental cycle times, or phase times, nor between sequence of replication and frequency with which segregant chromosomes are lost. We therefore conclude that the direction and extent of segregation is not directly determined by the interaction of parental cycle or phase times.

Animals↗

PubMed2004

Primitive auditory stream segregation: a neurophysiological study in the songbird forebrain.

Auditory stream segregation refers to the perceptual grouping of sounds, to form coherent representations of objects in the acoustic scene, and is a fundamental aspect of hearing and speech perception. The perceptual segregation of simple interleaved tone sequences has been studied in humans and European starlings (Sturnus vulgaris) using sequences of 2 alternating tones differing in frequency (ABA-ABA-ABA-...). The segregation of A and B tones into separate auditory streams is believed to be promoted by preattentive auditory processes that increase the separation of excitation patterns along a tonotopic gradient. We tested the hypothesis that frequency selectivity and forward masking operate as 2 preattentive processes in sequential stream segregation by recording neural responses in the auditory forebrain of awake starlings to repeated ABA- sequences in which we varied the frequency separation (DeltaF) between the A and B tones and the tone repetition time (TRT). The A tones were presented at the neurons' characteristic frequency (CF), and B tones differed from the CF over a one-octave range. Larger DeltaF values and shorter TRTs promote the perceptual segregation of alternating tone sequences in humans and also resulted in larger differences in neural responses to alternating CF (A) and non-CF (B) tones. Our results are consistent with the hypothesis that preattentive auditory processes, such as frequency selectivity and forward masking, contribute to the perceptual segregation of sequential acoustic events having different frequencies into separate auditory streams, but also suggest that additional processes may be required to account for all known perceptual effects related to sequential auditory stream segregation.

Acoustic Stimulation↗

PubMed1990

Development of the mammalian retinogeniculate pathway: target finding, transient synapses and binocular segregation.

This review is concerned with the development of the mammalian retinogeniculate projection from the perspective of our studies on the hamster and to a lesser extent on the cat. In these, and other mammalian species, axons from the two eyes initially spread throughout the dorsal lateral geniculate nucleus (dLGN) and thus completely overlap. Later they segregate, the axons from each eye coming to occupy discrete, non-overlapping territories within the dLGN. The process of segregation to establish the adult pattern coincides with the death of retinal ganglion cells projecting to inappropriate areas of the dLGN and with the loss, by degeneration or retraction, of the axons and/or axonal branches initially located within inappropriate territory of the dLGN. These events occur in the early postnatal period in hamsters, before the eyes have opened, and in cats and monkeys they occur entirely during embryonic life: thus, they do not depend on the onset of normal visual function. If one eye is removed before segregation has begun, the terminal fields of the crossed and uncrossed axons from the remaining eye do not segregate, suggesting that segregation in normal development may depend on some form of interaction between retinal ganglion cells from the two eyes. Attractive and/or repulsive influences exerted by the dLGN on retinogeniculate axons may also be involved in the formation of eye-specific territories. Experimental ultrastructural studies in hamster and cat show that the overlap phase is associated with the formation, by inappropriately located axons, of transient synapses similar to those made by retinogeniculate axons in appropriate parts of the dLGN. In the cat, the transient synapses are made by the axon trunk and by side branches of retinogeniculate axons with terminal arbors in appropriate parts of the nucleus; the transient synapses disappear as the side branches are shed or retracted during the segregation period. Because of good evidence that electrical activity of the retinogeniculate axons may be involved in binocular segregation of inputs, we suggest that the formation and elimination of transient synapses play a significant role in the development of the orderly retinogeniculate projections.

Aging↗

PubMed2004

Segregation of minorities in the metropolis: two decades of change.

Data from Census 2000 show that black-white segregation declined modestly at the national level after 1980, while Hispanic and Asian segregation rose in most metropolitan areas. Changes that may have produced greater changes for blacks proved to have insignificant effects: there was no net shift of the black population toward less-segregated areas, segregation at the metropolitan level did not decline more in areas where the incomes of blacks came closer to the incomes of whites over time, and the emergence of more multiethnic metropolises had no impact. As in the past, declines were centered in the South and West and in areas with smaller black populations. Increases in Hispanic and Asian segregation in individual metropolitan areas were counterbalanced by a net movement of these two groups toward areas of lower segregation. These increases were associated especially with the more rapid growth in the Hispanic and Asian populations. Hispanic segregation increased more in regions where group members had declining incomes relative to the incomes of whites and included a growing share of immigrants.

Black or African American↗

PubMed2003

Future directions in residential segregation and health research: a multilevel approach.

The authors examine the research evidence on the effect of residential segregation on health, identify research gaps, and propose new research directions. Four recommendations are made on the basis of a review of the sociological and social epidemiology literature on residential segregation: (1) develop multilevel research designs to examine the effects of individual, neighborhood, and metropolitan-area factors on health outcomes; (2) continue examining the health effects of residential segregation among African Americans but also initiate studies examining segregation among Hispanics and Asians; (3) consider racial/ethnic segregation along with income segregation and other metropolitan area factors such as poverty concentration and metropolitan governance fragmentation; and (4) develop better conceptual frameworks of the pathways that may link various segregation dimensions to specific health outcomes.

Demography↗

PubMed1989

Effect of segregation on prevention of intramammary infections by Staphylococcus aureus.

Effectiveness of segregating cows with Staphylococcus aureus intramammary infections was studied over 1 yr. Nine herds were split into control (n = 5) or segregated (n = 4) groups. Cows with S. aureus intramammary infections were milked last in segregated herds. Monthly milk samples were collected aseptically for microbiologic analysis. Mean incidences of S. aureus intramammary infections were 3.7 and 4.3 cases/100 cow-mo in segregated and control herds. The mean prevalence of S. aureus intramammary infections decreased in both segregated and control herds during the study. Mean percentages of cows with S. aureus intramammary infections at the beginning and end of the study were 33.7 and 21.5 in segregated herds and 25.3 and 15.0 in control herds. Cows in all herds with S. aureus intramammary infections were preferentially culled. There were no significant differences in incidence and prevalence of S. aureus intramammary infections between groups, suggesting that S. aureus intramammary infections can be controlled without segregation.

Animals↗