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PubMed1996

Single-parent segregant pools for allocation of markers to a specified chromosomal region in outcrossing species.

Bulked co-segregant analysis is a method of rapidly allocating unmapped genetic markers to a specific chromosomal region. Although originally developed for utilization in populations derived from crosses between fully inbred lines, it has been proposed that co-segregant pools could also serve the same purpose in outbreeding populations, if individuals from only a single large family are pooled. Large, fully mapped, single-sire backcross and half-sib families are presently available as part of the international chicken and bovine reference family panels respectively. In this study, power and tests of significance for single-parent co-segregant analysis are derived for full-sib, single-parent back-cross and single-parent half-sib families, as a function of proportion of recombination between index marker and linked marker, pro-portion of single-parent alleles among the mates, number of individuals in each segregant pool and technical error variance. Power was found to be greater than 0.80 for many reasonable parameter combinations. The method is illustrated using microsatellite markers and a large single-sire bovine family, part of the international bovine reference family panel.

Alleles↗
PubMed1996

HLA and leprosy: segregation and linkage study.

BACKGROUND: The presence of a genetic factor in the determination of leprosy has long been debated. This study tests whether the HLA-linked control of susceptibility to leprosy and/or for the types of leprosy could be confirmed. MATERIALS AND METHODS: In 15 multicase families, the method of DeVries et al., 1976, was used to detect nonrandom segregation of parental HLA haplotypes in their affected and healthy siblings. Linkage analyses, for two and three alleles were performed by the computer program LIPED: RESULTS: For the affected siblings, the segregations of the parental HLA haplotype were significantly nonrandom from the healthy parents and random from the affected parents, indicating that affected siblings were sharing their HLA haplotypes (segregated from the healthy parents) more than expected. The segregations to the healthy siblings from both the healthy and affected parents were random. Healthy siblings inherited the haplotypes shared among the leprosy siblings randomly as expected. There were excess DR2/DR2 homozygote individuals among tuberculoid siblings. The highest lod score was achieved when we considered our suggested three-alleles model for the susceptibility to the different types of leprosy. CONCLUSIONS: A closely HLA-linked gene on chromosome number 6 with multiple alleles (3 or more) in recombination fraction between 0.05 and 0.1 with 70 to 100% penetrance may be responsible for the susceptibility to the different types of leprosy, whereas the susceptibility to leprosy per se maybe the responsibility of non-HLA linked gene/s. DR2/DR2 homozygote individuals may be relatively at high risk of developing leprosy or tuberculoid leprosy.

Alleles↗
PubMed2004

Uneven segregation of sporophytic self-incompatibility alleles in Arabidopsis lyrata.

Self-incompatibility in Arabidopsis lyrata is sporophytically controlled by the multi-allelic S-locus. Self-incompatibility alleles (S-alleles) are under strong negative frequency dependent selection because pollen carrying common S-alleles have fewer mating opportunities. Population genetics theory predicts that deleterious alleles can accumulate if linked to the S-locus. This was tested by studying segregation of S-alleles in 11 large full sib families in A. lyrata. Significant segregation distortion leading to an up to fourfold difference in transmission rates was found in six families. Differences in transmission rates were not significantly different in reciprocal crosses and the distortions observed were compatible with selection acting at the gametic stage alone. The S-allele with the largest segregation advantage is also the most recessive, and is very common in natural populations concordant with its apparent segregation advantage. These results imply that frequencies of S-alleles in populations of A. lyrata cannot be predicted based on simple models of frequency-dependent selection alone.

Alleles↗
PubMed2003

Racial segregation and longevity among African Americans: an individual-level analysis.

OBJECTIVE: To test the relationship between racial segregation and mortality using a multidimensional questionnaire-based measure of exposure to segregation. DATA SOURCES: Data for this analysis come from the National Survey of Black Americans (NSBA), a national multistage probability sample of 2,107 African Americans (aged 18-101). The NSBA was conducted as a household survey. The NSBA was matched with the National Death Index (NDI). STUDY DESIGN: Prospective cohort study, where Cox regression analysis was used to examine the effect of baseline variables on time to death over a 13-year period. PRINCIPAL FINDINGS: Respondents who were exposed to racial segregation were significantly less likely to survive the study period after controls for age, health status, and other predictors of mortality. CONCLUSION: The results support previous studies linking segregation with health outcomes.

Adolescent↗
PubMed1998

Segregation pattern of kanamycin resistance marker in Azotobacter vinelandii did not show the constraints expected in a polyploid bacterium.

It was suggested that Azotobacter vinelandii cells contain about 80 copies of their chromosome and when foreign genes are introduced into the cell, it took several generations for them to spread to all 80 chromosomes even in the presence of selection. In contrast, the fact that many recessive mutants can be isolated from A. vinelandii without the constraints expected for a cell that has 80 copies of its chromosome argued against this organism being highly polyploid. We have investigated the segregation of a kanamycin resistant genetic marker under non-selective conditions in A. vinelandii. Plasmid DNA was used to introduce the kanamycin resistance gene onto the A. vinelandii chromosome at the nifY locus by homologous recombination. The transformants were identified from non-transformants with the aid of replica plating, and hence the colonies examined for segregation of the genetic marker were never subjected to kanamycin selection. In spite of growing the transformants in the absence of selection pressure, no segregant that lacked the kanamycin resistance gene was scored. These analyses suggested that the segregation of the kanamycin marker in A. vinelandii did not exhibit any constraints expected in a highly polyploid bacterium.

Azotobacter vinelandii↗
PubMed2002

Auditory stream segregation on the basis of amplitude-modulation rate.

In this study, auditory stream segregation based on differences in the rate of envelope fluctuations--in the absence of spectral and temporal fine structure cues--was tested. The temporal sequences to segregate were composed of fully amplitude-modulated (AM) bursts of broadband noises A and B. All sequences were built by the reiteration of a ABA triplet where A modulation rate was fixed at 100 Hz and B modulation rate was variable. The first experiment was devoted to measuring the threshold difference in AM rate leading subjects to perceive the sequence as two streams as opposed to just one. The results of this first experiment revealed that subjects generally perceived the sequences as a single perceptual stream when the difference in AM rate between the A and B noises was smaller than 0.75 oct, and as two streams when the difference was larger than about 1.00 oct. These streaming thresholds were found to be substantially larger than, and not related to, the subjects' modulation-rate discrimination thresholds. The results of a second experiment demonstrated that AM-rate-based streaming was adversely affected by decreases in AM depth, but that segregation remained possible as long as the AM of either the A or B noises was above the subject's AM-detection threshold. The results of a third experiment indicated that AM-rate-based streaming effects were still observed when the modulations applied to the A and B noises were set individually, either at a constant level in dB above AM-detection threshold, or at levels at which they were of the same perceived strength. This finding suggests that AM-rate-based streaming is not necessarily mediated by perceived differences in AM depth. Altogether, the results of this study indicate that sequential sounds can be segregated on the sole basis of differences in the rate of their temporal fluctuations in the absence of other temporal or spectral cues.

Adult↗
PubMed2003

Perceptual segregation of competing speech sounds: the role of spatial location.

Culling and Summerfield [J. Acoust Soc. Am. 92, 785-797 (1995)] showed that listeners could not use ongoing interaural time differences (ITDs) to achieve source segregation. The present experiments tested a free-field analog of their experiment. The stimuli consisted of narrow bands of noise, pairs of which represented the first and second formants of the whispered vowels "ar," "ee," "er," and "oo." A target noise-band pair (vowel) was presented at various angles on the listeners' left while a complementary distracter was presented on the listeners' right. Listeners correctly identified the target vowel in the free-field well above chance. Performance remained well above chance in headphone experiments that retained spatial cues but eliminated reverberations and head movements. The full range of cues that normally determine perceived spatial location provided sufficient information for segregation. Further experiments, which systematically evaluated the contribution of these cues in isolation and in combination, showed that some listeners, following training, exhibited the ability to segregate based on ongoing ITDs alone. Substantial individual differences were observed. The results show that listeners can use spatial cues to segregate simultaneous sound sources.

Adolescent↗
PubMed2004

Auditory stream segregation in monkey auditory cortex: effects of frequency separation, presentation rate, and tone duration.

Auditory stream segregation refers to the organization of sequential sounds into "perceptual streams" reflecting individual environmental sound sources. In the present study, sequences of alternating high and low tones, "...ABAB...," similar to those used in psychoacoustic experiments on stream segregation, were presented to awake monkeys while neural activity was recorded in primary auditory cortex (A1). Tone frequency separation (AF), tone presentation rate (PR), and tone duration (TD) were systematically varied to examine whether neural responses correlate with effects of these variables on perceptual stream segregation. "A" tones were fixed at the best frequency of the recording site, while "B" tones were displaced in frequency from "A" tones by an amount = delta F. As PR increased, "B" tone responses decreased in amplitude to a greater extent than "A" tone responses, yielding neural response patterns dominated by "A" tone responses occurring at half the alternation rate. Increasing TD facilitated the differential attenuation of "B" tone responses. These findings parallel psychoacoustic data and suggest a physiological model of stream segregation whereby increasing delta F, PR, or TD enhances spatial differentiation of "A" tone and "B" tone responses along the tonotopic map in A1.

Acoustic Stimulation↗
PubMed2006

Monaural speech segregation using synthetic speech signals.

When listening to natural speech, listeners are fairly adept at using cues such as pitch, vocal tract length, prosody, and level differences to extract a target speech signal from an interfering speech masker. However, little is known about the cues that listeners might use to segregate synthetic speech signals that retain the intelligibility characteristics of speech but lack many of the features that listeners normally use to segregate competing talkers. In this experiment, intelligibility was measured in a diotic listening task that required the segregation of two simultaneously presented synthetic sentences. Three types of synthetic signals were created: (1) sine-wave speech (SWS); (2) modulated noise-band speech (MNB); and (3) modulated sine-band speech (MSB). The listeners performed worse for all three types of synthetic signals than they did with natural speech signals, particularly at low signal-to-noise ratio (SNR) values. Of the three synthetic signals, the results indicate that SWS signals preserve more of the voice characteristics used for speech segregation than MNB and MSB signals. These findings have implications for cochlear implant users, who rely on signals very similar to MNB speech and thus are likely to have difficulty understanding speech in cocktail-party listening environments.

Adult↗
PubMed1964

DNA SEGREGATION IN ESCHERICHIA COLI: OBSERVATIONS BY MEANS OF TRITIATED THYMIDINE DECAY.

Escherichia coli, strain 15(T-L-), inactivation by H(3)-thymidine decay was used in a study of DNA segregation. Two characteristics of the inactivation curves due to H(3)-thymidine decay, the initial slope and stable fraction, enable the mode of segregation to be defined. The results suggest that the segregation pattern is consistent with a semiconservative model of DNA replication. The data on the stable fraction indicate that the DNA of strain 15(T-L-), under our experimental conditions, may be organized into one duplex structure. Since colony-forming ability was used as the means of assay, it is possible to compare these experiments with those in which DNA segregation is examined on a structural basis.

DNA↗
PubMed2000

Necessity for afferent activity to maintain eye-specific segregation in ferret lateral geniculate nucleus.

In the adult mammal, retinal ganglion cell axon arbors are restricted to eye-specific layers in the lateral geniculate nucleus. Blocking neuronal activity early in development prevents this segregation from occurring. To test whether activity is also required to maintain eye-specific segregation, ganglion cell activity was blocked after segregation was established. This caused desegregation, so that both eyes' axons became concentrated in lamina A, normally occupied only by contralateral afferents. These results show that an activity-dependent process is necessary for maintaining eye-specific segregation and suggest that activity-independent cues may favor lamina A as the target for arborization of afferents from both eyes.

Aminobutyrates↗
PubMed1986

An alternative pathway for meiotic chromosome segregation in yeast.

In meiosis I of most organisms, homologous chromosomes pair, recombine, and then segregate to opposite poles of the cell. Crossing-over is normally necessary to ensure the proper segregation of the homologs. Recently developed techniques have made it possible to study meiosis with highly defined artificial chromosomes. These techniques were used to demonstrate the existence of a system capable of segregating pairs of nonrecombined artificial chromosomes, regardless of the extent of their sequence homology. This system may contribute to the high fidelity of meiosis by mediating the segregation of pairs of natural chromosomes that have failed to recombine.

Chromosomes↗
PubMed1986

Plasmid segregation into minicells is associated with membrane attachment and independent of plasmid replication.

The role of plasmid replication in the segregation of plasmids into Escherichia coli minicells was investigated with temperature-sensitive replication mutants derived from E. coli plasmids ColE1 and pSC101. For as long as six generations of growth, at permissive or nonpermissive temperatures (when greater than 80% of plasmid replication was inhibited), the same amount of previously 3H-labeled plasmid DNA segregated into minicells. Density gradient separations of wild-type and temperature-sensitive plasmid DNA from both replicons segregated into the minicells showed that about 20 to 25% was stably associated with the minicell membrane at both temperatures. Electron microscopy showed this DNA to consist of circular plasmid molecules attached to the minicell membrane. These combined findings suggest that segregation of plasmids into minicells and their association with the minicell membrane are interrelated and independent of plasmid replication.

Adhesiveness↗
PubMed1989

Chromosome and cell wall segregation in Streptococcus faecium ATCC 9790.

Segregation was studied by measuring the positions of autoradiographic grain clusters in chains formed from single cells containing on average less than one radiolabeled chromosome strand. The degree to which chromosomal and cell wall material cosegregated was quantified by using the methods of S. Cooper and M. Weinberger, dividing the number of chains labeled at the middle. This analysis indicated that in contrast to chromosomal segregation in Escherichia coli and, in some studies, to that in gram-positive rods, chromosomal segregation in Streptococcus faecium was slightly nonrandom and did not vary with growth rate. Results were not significantly affected by strand exchange. In contrast, labeled cell wall segregated predominantly nonrandomly.

Autoradiography↗
PubMed1966

Gene recombination and segregation of resistance factor R in Escherichia coli.

Hashimoto, Hajime (Osaka University, Osaka, Japan), and Yukinori Hirota. Gene recombination and segregation of resistance factor R in Escherichia coli. J. Bacteriol. 91:51-62. 1966.-Independent chloramphenicol-sensitive (CM(s)) mutants of the drug-resistance factor R were isolated. Introduction of two different R factor CM(s) mutants into a single bacterium, by conjugation or transduction, gave chloramphenicol-resistant (CM(r)) colonies when such strains were plated on a medium containing chloramphenicol (Cm). These CM(r) colonies resulted from recombination between two R factors contained within the same cell. Most of the CM(r) colonies were heterogeneous, and segregation of drug-resistance markers was observed among the progeny. Segregated bacteria which still carried the recombinant R factor were stable for resistance to Cm as well as for other markers of R. All the markers of recombinant R factors were cotransducible with high coincidence and at the same frequency as wild-type R. Sensitive mutants of R which had lost all the resistance markers of the R factor were found also. A mutation of R, referred to as SMA, which was sensitive to streptomycin and sulfanilamide, was capable of reverting to resistance to both of these drugs simultaneously. The sensitive alleles for SMA, CM, and TC were shown to be recessive to the resistance alleles. Mutants of R having multisite mutations or deletions in the CM gene were isolated and used to analyze the pattern of linked segregation of unselected markers of the recombinant R factor. The drug resistance factor R was shown to have two linkage groups, CM-SMA and TC-m.

Chloramphenicol↗
PubMed1993

Investigation of inheritance of chronic inflammatory bowel diseases by complex segregation analysis.

OBJECTIVE: To investigate the mode of inheritance of ulcerative colitis and Crohn's disease by complex segregation analysis. DESIGN: Cross sectional population based survey of familial occurrence of chronic inflammatory bowel disease. SETTING: Population of the Copenhagen county in 1987. SUBJECTS: 662 patients in whom inflammatory bowel disease had been diagnosed before 1979, of whom 637 (96%) provided adequate information. Of 504 patients with ulcerative colitis, 54 had 77 relatives with ulcerative colitis and of 133 patients with Crohn's disease, five had seven relatives with Crohn's disease. MAIN OUTCOME MEASURES: Patterns of segregation of either disease as assessed by complex segregation analysis performed with the computer program POINTER. RESULTS: The analysis suggested that a major dominant gene with a penetrance of 0.20-0.26 is present in 9-13% of adult patients with ulcerative colitis. The analysis did not allow for other components in the familial aggregation. For Crohn's disease the best fitting model included a major recessive gene with complete penetrance, for which 7% of the patients are homozygous. However, this model was not significantly different from a multifactorial model. CONCLUSIONS: The segregation pattern indicates that a major dominant gene has a role in ulcerative colitis, and suggests that a major recessive gene has a role in Crohn's disease.

Adolescent↗
PubMed2004

Racial segregation and county level intentional injury in Pennsylvania: analysis of hospital discharge data for 1997-1999.

STUDY OBJECTIVE: This study examined whether high levels of racial segregation are associated with high county level intentional injury rates. DESIGN: Multiple linear regression was used to assess the association between county racial segregation (measured by the Gini coefficient) and intentional injury rates. Multicollinearity was assessed with Eigenvalues and condition indices. SETTING: State of Pennsylvania. PATIENTS: County level intentional injury rates for 1995 to 1997 were calculated from hospital discharge data. MAIN RESULTS: After controlling for other known county level risk factors, higher levels of racial segregation in a county were significantly related to higher intentional injury rates. Multicollinearity was not a problem. Population size and density, family stability and median income, together with the percentage male, unemployed, in poverty, divorced men, and high school graduates of the county were controlled. CONCLUSIONS: Racial segregation is an important factor in the rate of intentional injury in a community. These results may be important for municipal and state agencies when developing public policies to prevent violence and promote racial integration.

Adult↗
PubMed1978

Segregation analysis of chronic childhood spinal muscular atrophy.

A formal segregation analysis for the disease 'chronic childhood spinal muscular atrophy' is presented. This disease is also known as 'Kugelberg-Welander disease', 'arrested Werdnig-Hoffmann disease', and 'chronic proximal or generalised spinal muscular atrophy'. There were 124 index cases occurring in 115 families. Ascertainment of index patients was by incomplete multiple selection. Three types of segregation analysis were performed: Weinberg Proband, an improved Weinberg Proband with a variance corrected formula for differences both in family size and ascertainment probability and a backeting technique assuming the extremes of both single and of truncate selection. All three methods gave similar results. The improved Weinberg Proband method with corrections for differences in ascertainment and in family size gave a segregation ratio of 0.18 and a 95% confidence range of 0.11 to 0.25. The mid-point of the bracketing method assuming extremes of truncate and of single selection was 0.19. The segregation ratio of that group of children with clinical onset before 9 months of age was 0.21, which does not differ significantly from the 0.25 predicted on the basis of autosomal recessivity. Evidence is presented to indicate that 25% of index patients may be due to new dominant mutations, or phenocopies, or both, and that these occur particularly among sporadic cases with clinical onset over 2 years of age. Empirical risk figures for use in genetic counselling are presented, and the literature of the subject is reviewed.

Child, Preschool↗