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PubMed1999

Fission yeast mutants that alleviate transcriptional silencing in centromeric flanking repeats and disrupt chromosome segregation.

In the fission yeast Schizosaccharomyces pombe genes are transcriptionally silenced when placed within centromeres, within or close to the silent mating-type loci or adjacent to telomeres. Factors required to maintain mating-type silencing also affect centromeric silencing and chromosome segregation. We isolated mutations that alleviate repression of marker genes in the inverted repeats flanking the central core of centromere I. Mutations csp1 to 13 (centromere: suppressor of position effect) defined 12 loci. Ten of the csp mutants have no effect on mat2/3 or telomere silencing. All csp mutants allow some expression of genes in the centromeric flanking repeat, but expression in the central core is undetectable. Consistent with defective centromere structure and function, chromosome loss rates are elevated in all csp mutants. Mutants csp1 to 6 are temperature-sensitive lethal and csp3 and csp6 cells are defective in mitosis at 36 degrees. csp7 to 13 display a high incidence of lagging chromosomes on late anaphase spindles. Thus, by screening for mutations that disrupt silencing in the flanking region of a fission yeast centromere a novel collection of mutants affecting centromere architecture and chromosome segregation has been isolated.

Centromere↗
PubMed2000

Genotypic stability, segregation and selection in heteroplasmic human cell lines containing np 3243 mutant mtDNA.

The mitochondrial genotype of heteroplasmic human cell lines containing the pathological np 3243 mtDNA mutation, plus or minus its suppressor at np 12300, has been followed over long periods in culture. Cell lines containing various different proportions of mutant mtDNA remained generally at a consistent, average heteroplasmy value over at least 30 wk of culture in nonselective media and exhibited minimal mitotic segregation, with a segregation number comparable with mtDNA copy number (>/=1000). Growth in selective medium of cells at 99% np 3243 mutant mtDNA did, however, allow the isolation of clones with lower levels of the mutation, against a background of massive cell death. As a rare event, cell lines exhibited a sudden and dramatic diversification of heteroplasmy levels, accompanied by a shift in the average heteroplasmy level over a short period (<8 wk), indicating selection. One such episode was associated with a gain of chromosome 9. Analysis of respiratory phenotype and mitochondrial genotype of cell clones from such cultures revealed that stable heteroplasmy values were generally reestablished within a few weeks, in a reproducible but clone-specific fashion. This occurred independently of any straightforward phenotypic selection at the individual cell-clone level. Our findings are consistent with several alternate views of mtDNA organization in mammalian cells. One model that is supported by our data is that mtDNA is found in nucleoids containing many copies of the genome, which can themselves be heteroplasmic, and which are faithfully replicated. We interpret diversification and shifts of heteroplasmy level as resulting from a reorganization of such nucleoids, under nuclear genetic control. Abrupt remodeling of nucleoids in vivo would have major implications for understanding the developmental consequences of heteroplasmy, including mitochondrial disease phenotype and progression.

Base Sequence↗
PubMed2001

A general polyploid model for analyzing gene segregation in outcrossing tetraploid species.

Polyploidy has played an important role in higher plant evolution and applied plant breeding. Polyploids are commonly categorized as allopolyploids resulting from the increase of chromosome number through hybridization and subsequent chromosome doubling or autopolyploids due to chromosome doubling of the same genome. Allopolyploids undergo bivalent pairing at meiosis because only homologous chromosomes pair. For autopolyploids, however, all homologous chromosomes can pair at the same time so that multivalents and, therefore, double reductions are formed. In this article, we use a maximum-likelihood method to develop a general polyploid model for estimating gene segregation patterns from molecular markers in a full-sib family derived from an arbitrary polyploid combining meiotic behaviors of both bivalent and multivalent pairings. Two meiotic parameters, one describing the preference of homologous chromosome pairing (expressed as the preferential pairing factor) typical of allopolyploids and the other specifying the degree of double reduction of autopolyploids, are estimated. The type of molecular markers used can be fully informative vs. partially informative or dominant vs. codominant. Simulation studies show that our polyploid model is well suited to estimate the preferential pairing factor and the frequency of double reduction at meiosis, which should help to characterize gene segregation in the progeny of autopolyploids. The implications of this model for linkage mapping, population genetic studies, and polyploid classification are discussed.

Crosses, Genetic↗
PubMed1974

Some radiation effects on segregation in Drosophila.

Translocation induced in the immature oocyte, in meiotic prophase, affects division I orientation and segregation, the usual result being that the two halves of translocations are directed to opposite poles. Since interchange is usually (if not exclusively) between chromatids, this is to be expected from the creation of illegitimate conjunctions. Good agreement is obtained between patterns of segregations deduced from recovered half-translocation bearing exceptions and the kinds of disomic gametes expected as alternative recoveries from the same division I configurations. Inferences drawn from the study of compound-X females have been found to apply as well in the case of females of normal karyotype. Numerical errors occur predominantly, possibly exclusively, in division I. The rate of induced nondisjunction of specific chromosome pairs varies in relation to the structure of the entire complement, as required if radiation-induced nondisjunction is interchange dependent, but which would be unexpected if the mechanism involved effects on individual spindle fibers, chromosomes, or chromosomal bivalents.

Animals↗
PubMed1980

Genetic dissection of segregation distortion. III. Unequal recovery of reciprocal recombinants.

The genetic structure of a segregation distorter chromosome (a derivative of SD-36) has been analyzed in a system in which recombination in the second chromosome is blocked by inversions except for the critical region around the centromeric heterochromatin. The results confirm the map order and characteristics of four loci known to be involved in segregation distortion, namely Sd, E(SD), Rspins, M(SD). However, SD-36 carries a fifth major locus involved in distortion. This locus is near pr in 2L and has the effect of enhancing the degree of distortion. In addition, reciprocal recombinant products from SD-36 are recovered unequally. All recombinants carrying the pr region from SD-36 seem also to carry Sd, although Sd has previously been mapped 1.6 units to the left of pr. Both the enhancement of distortion and the unequal recovery of reciprocal products can be explained if it is assumed that the new locus near pr in SD-36 is actually a duplication of Sd.

Animals↗
PubMed1996

Aging and the segregation of auditory stimulus sequences.

This study aimed to clarify whether the age-related decline in selective attention widely reported in the literature can be attributed to a selective deficit in the segregation of relevant streams of sound from irrelevant ones. Young and older individuals responded to infrequent deviant stimuli (targets) mixed with distractors in situations that facilitated perception of one or two streams of sounds. Both young and older adults showed the same degree of improvement in performance under conditions that promoted auditory streaming. However, in both listening conditions young subjects were faster and more accurate than older subjects in responding to target zones. Thus, it appears that age-related declines in auditory selective attention cannot be attributed to a selective deficit in the segregation of auditory sequences, but occur in a subsequent stage of processing such as response selection and/or execution.

Acoustic Stimulation↗
PubMed1975

Patterns of contacts for residents of age-segregated and age-integrated housing.

It has been suggested that age-segregated housing for the elderly is undesirable because elderly need contact with, and stimulation from, the young. Research has shown that, even in age-integrated housing, intergenerational contact is normally limited and greater density of age peers will lead to more opportunities for contacts and friendships. Interviews with residents of six retirement facilities and with matched controls in age-integrated housing showed that test residents interacted less than their controls with their children, grandchildren, and other relatives, and fewer had friends younger than 40. Test residents had, relative to their controls, more new friends and visited more with neighbors and with age-peer friends. Very little test-control difference was found on sufficiency of contact. A 2-year follow-up interview showed substantially the same patterns. It was concluded that age-segregated housing does imply different spheres of contacts but that either situation can be satisfactory for person who has freely made the choice.

Age Factors↗
PubMed1993

Segregation of delta F508 and normal CFTR alleles in human sperm.

Single sperm typing provides an accurate method to order tightly linked loci by single cell DNA high resolution segregation analysis. We have used similar methods to type individual sperm from a known delta F508 cystic fibrosis heterozygote to determine the frequency of the mutation within his germ cell population, and to test possible explanations for the reported sex ratio distortion of the cystic fibrosis (CF) mutation to male offspring. Using a nested polymerase chain reaction we have been able to amplify a single locus sequence, cystic fibrosis transmembrane conductance regulator (CFTR), from a single target sperm haploid genome to detectable amounts without the use of radioactivity. The same sperm from a single male delta F508 carrier were simultaneously typed for the presence of the sex chromosomes to verify the ratio of X- to Y-bearing sperm and to determine the association, if any, between sex and delta F508 in male gametes. We have demonstrated that there is a significant difference in the proportions of 'normal' and 'delta F508' sperm (X2 = 7.36, p < 0.01), although when the same sperm are sexed the difference between delta F508/X and delta F508/Y sperm is not significant (X2 = 1.71, p = 0.192). Single sperm typing can address questions about segregation distortion in man, and it is unlikely that sex ratio distortion for CF carriers is due to events which occur pre-fertilisation. As these data are from one individual only, they should be confirmed for other male carriers, including those with different CF mutations.

Alleles↗
PubMed1999

A chromosome 4p haplotype segregating with Parkinson's disease and postural tremor.

We investigated a large family with levodopa-responsive, Lewy body parkinsonism in which the disease segregates as an apparent autosomal dominant trait. After performing a genome screen, we identified a chromosome 4p haplotype that segregates with the disease. However, this haplotype also occurs in individuals in the pedigree who do not have clinical Lewy body parkinsonism but rather suffer from postural tremor, consistent with essential tremor. These data demonstrate a new locus for Lewy body parkinsonism and suggest that in some circumstances postural tremor can be an alternative phenotype of the samepathogenic mutation as Lewy body parkinsonism.

Chromosome Mapping↗
PubMed1980

HLA segregation of tuberculoid leprosy: confirmation of the DR2 marker.

Families with multiple cases of leprosy were tested for HLA (histocompatibility leukocyte antigen)-linked control of susceptibility to tuberculoid leprosy and association with HLA-DR2. Thirty-one non-HLA genetic markers were also examined for indications of non-HLA-linked genetic factors that might control susceptibility to tuberculoid leprosy. A significant (P = 0.002) preferential inheritance of HLA-DR2 by siblings affected with tuberculoid leprosy, but not by healthy siblings nor by siblings affected with lepromatous leprosy, was observed. In addition, combined family data showed a significant (P less than 0.0025) excess of identical HLA haplotypes inherited from healthy parents by siblings affected with tuberculoid leprosy. Segregation on non-HLA polymorphisms did not deviate significantly from what would have occured randomly. These data are compatible with a recessive inheritance of HLA-linked susceptibility to tuberculoid leprosy. The preferential segregation of DR2 observed in children with tuberculoid leprosy (P less than 0.001 for the combined data from India) indicates that the HLA-linked susceptibility gene is either DR2 or in linkage disequilibrium with it.

Epitopes↗
PubMedDate not supplied

Genetic control of the honey bee (Apis mellifera) dance language: segregating dance forms in a backcrossed colony.

We studied the genetic control of the dance dialects that exist in the different subspecies of honey bees (Apis mellifera) by observing the variation in dance form observed in a backcross between two lines that showed widely different dance dialects. To do this we generated the reciprocal of the cross performed by Rinderer and Beaman (1995), thus producing phenotypic segregation of dance forms within a single colony rather than between colonies. Our results are consistent with Rinderer and Beaman (1995) in that inheritance of the transition point from round dancing --> waggle dancing is consistent with control by a single locus with more than one allele. That is, we found one dance type to be dominant in the F(1), and observed a 1:1 segregation of dance in a backcross involving the F(1) and the recessive parent. However, we found some minor differences in dance dialect inheritance, with the most significant being an apparent reversal of dominance between our cross (for us "black" is the dominant dialect) and that of Rinderer and Beaman (1995) (they report "yellow" to be the dominant dialect). We also found that our black bees do not perform a distinct sickle dance, whereas the black bees used by Rinderer and Beaman (1995) did perform such a dance. However, our difference in dominance need not contradict the results of Rinderer and Beaman (1995), as there is no evidence that body color and dominance for dance dialect are linked.

Animal Communication↗
PubMed1992

Segregation analysis of esophageal cancer in 221 high-risk Chinese families.

BACKGROUND: Until recently, environmental factors were considered of greatest importance in the etiology of esophageal cancer. Recent studies, however, have suggested that genetic factors also have a role. PURPOSE: Since no formal genetic study of this cancer has been previously reported, we carried out a statistical analysis to determine how important genetic factors are in the etiology of esophageal cancer in high-incidence areas of North China. METHODS: Using a logistic regressive model, we performed a segregation analysis on 221 high-risk nuclear families from the Yaocun Commune, Linxian, Henan Province of China, with at least one affected family member and with all offspring aged 40 years or older. Three models, the mendelian, the environmental, and the no-transmission models, were each compared with the general-transmission model that incorporated both genetic and environmental factors. RESULTS: According to Akaike's Information Criterion, the mendelian model provided the best fit for the data. By the chi-square test, the mendelian inheritance model was not rejected, but the environmental and the no-transmission models were both rejected. CONCLUSION: The segregation analysis indicated an autosomal recessive mendelian inheritance, with the alleged mendelian gene present at a frequency of 19%, causing 4% of this population to be predisposed to develop esophageal cancer. Large, unmeasured, residual familial factors, however, were also significant. IMPLICATIONS: Both an autosomal recessive gene and unexplained environmental factors appear to be important in the etiology of esophageal cancer in the subpopulation studied.

China↗
PubMed1996

Analysis of chromosome segregation in cytokinesis-blocked human lymphocytes: non-disjunction is the prevalent damage resulting from low dose exposure to spindle poisons.

The chromosome malsegregation pattern produced by the spindle poisons vinblastine (VBL) and colchicine (COL) in human lymphocytes was investigated. For this purpose, the fluorescence in situ hybridization with centromeric DNA probes for chromosomes X and 1 was applied to cell cultures treated with cytochalasin B, a cytokinesis-blocking agent. With this method, chromosome segregation in daughter nuclei - retained in the same envelope - can be easily analysed, simultaneously determining the loss and non-disjunction of specific chromosomes. Preliminary experiments demonstrated that the aneugenic effects elicited by low dose exposure to spindle poisons were effectively detected with treatments from the S/G2 phase (43 h) to harvest of cell cultures (60 or 72 h), with no drug-free medium recovery. This exposure protocol was used in subsequent experiments, where COL and VBL were applied at concentrations which had no effect on the cell cycle ranging to producing marked mitotic block. To account for sex differences in chromosome X instability, lymphocyte cultures from both male and female donors were used to study X chromosome malsegregation. Chromosome 1 malsegregation, however, was analysed in female lymphocytes only. VBL induced reproducible, significant increases of micronuclei in cytokinesis-blocked cells at 5 ng/ml and over. In female lymphocytes, chromosome X loss was observed at 5 ng/ml whereas chromosome 1 loss was only observed at 10 ng/ml. In male lymphocytes, no significant chromosome loss was observed. On the other hand, non-disjunction of both chromosomes X and 1 was effectively induced in female lymphocytes even at 1.25 ng/ml, the lowest dose tested. In male lymphocytes, non-disjunction of chromosome X was observed at 5 ng/ml. Treatments with COL produced a significant increase of micronucleated cells only at the highest dose tested (20 ng/ml). No significant increase in the incidence of either chromosome X or chromosome 1 loss was observed. With cell cultures from donors of both genders, a significant increase in non-disjunction of chromosome X was observed at 5 ng/ml. At the same dose, chromosome 1 non-disjunction significantly increased. These results suggest that in cytokinesis-blocked human lymphocytes, non-disjunction is the prevalent error in chromosome segregation induced by low dose exposure to spindle poisons. Interestingly, non-disjunction was effectively induced even at doses which did not produce detectable detrimental effects on the cell cycle.

Aneuploidy↗
PubMed1986

Linkage arrangement in the vitellogenin gene family of Xenopus laevis as revealed by gene segregation analysis.

Using restriction fragment length polymorphism (RFLP) we have analyzed the segregation of alleles of the different vitellogenin genes of Xenopus laevis. The results demonstrate that the four genes whose expression is controlled by oestrogen, form two linkage groups. The genes A1, A2 and B1 are linked genetically whereas the fourth gene, the gene B2, segregates independently. The possible origin of this unexpected arrangement is discussed.

Alleles↗
PubMed1989

Rapid segregation of heteroplasmic bovine mitochondria.

By following the transmission of a heteroplasmic mitochondrial DNA mutation through four generations of Holstein cows, we have documented that substantial shifts in the levels of heteroplasmy can occur between single mammalian generations, that neutral mitochondrial genotypes can segregate in different directions in offspring of the same female, and that a return to homoplasmy may occur in only two or three generations. This apparently rapid rate of mitochondrial DNA segregation in mammals contrasts to the much slower rates observed previously in insects and suggest fundamental differences between taxa regarding the mechanisms of mitochondrial gene transmission.

Animals↗
PubMed1995

Consequences of non-extrusion of the first polar body and control of the sequential segregation of homologues and chromatids in mammalian oocytes.

Absence of polar body formation, or premature chromatin condensation (PCC) in human oocytes can cause infertility. We studied in-vitro maturing mouse oocytes in order to identify risk factors for such conditions, and for the precocious segregation of homologues or chromatids. Treatment with the actin-binding drug cytochalasin D (10 micrograms/ml) arrested oocytes in metaphase I. Upon exposure to Ca(2+)-ionophores, anaphase I was triggered in the absence of cytokinesis. Chiasmata resolved and homologues separated instantaneously. In some oocytes predivision of all chromatids occurred. Homologues or chromatids never separated even after exposure to Ca(2+)-ionophores when microtubules were depolymerized, although bivalents could eventually decondense. Thus, in meiosis I checkpoints exist which ensure that homologue separation only takes place when a metaphase I spindle is present but cytokinesis and anaphase progression can be uncoupled. Cycloheximide induced a sequential separation of homologues in oocytes with intact metaphase I spindle, resulting in metaphase II chromosomes and bivalents in individual cells as also found in some human oocytes of aged females. In oocytes which progressed to metaphase II but failed to extrude a first polar body, the two sets of chromosomes eventually aligned on a common spindle ('diploid' metaphase II). PCC of one set was never observed. Ageing in vitro of cytochalasin D-blocked metaphase I oocytes had no pronounced effect on chromosome segregation.

Actins↗
PubMed1980

Studies on rat liver catalase. XI. Site of synthesis and segregation by stripped ER membranes.

We reinvestigated the site of synthesis of rat liver catalase, and it has been reconfirmed that catalase is synthesized not only by free polysomes but also by membrane-bound polysomes. Considerable amounts of nascent catalase on rough microsomes were released from the membrane into the medium upon incubation with puromycin, not transported directly into the intracisternal cavity of microsomes. On the other hand, catalase newly synthesized in vitro was shown to be segregated by stripped rat liver microsomal membranes in a state resistant to proteolysis. Since this segregation occurred without coupled protein synthesis, catalase appears to be transported by a mechanism different from co-translational transfer. A hypothesis is presented regarding the mechanism of intracellular transport of liver catalase.

Animals↗
PubMedDate not supplied

Erythrocyte alloantigens in the Storrs strain of hereditary muscular dystrophic chickens and segregating testcross progeny.

The Storrs strain of muscular dystrophic chickens were typed for erythrocyte alloalleles at 10 loci, including the B locus. Gene fixation is present at five loci and expression of the predominate alloantigen varied in frequency from 0.53 to 0.91 at the other five loci tested. The Storrs strain of muscular dystrophic chickens are not fixed at the B locus, expressing the B2/B2 allelic combination 81 percent of the time and B2/B23 the remaining percentage. Testcross progeny segregating for the muscular dystrophy trait did not show any alloantigen associations at the 10 loci examined. No association of the MD train with a particular B genotype could be ascertained. CPK levels as a measure of muscle destruction in the muscular dystrophic testcross progeny segregating at the B locus did not reveal an association with any B haplotype. Serum IgG levels and low Con A response in muscular dystrophic testcross progeny also were not associated with any specific B locus alloantigen combinations. The possibility remains that the establishment of a pathological index for muscular dystrophy in MD chickens may reveal an association with the B locus.

Animals↗