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B Degen

Publications and source records attributed to B Degen.

12 recordsLinked to original sources
PubMed2005

Optimal sampling strategy for estimation of spatial genetic structure in tree populations.

Fine-scale spatial genetic structure (SGS) in natural tree populations is largely a result of restricted pollen and seed dispersal. Understanding the link between limitations to dispersal in gene vectors and SGS is of key interest to biologists and the availability of highly variable molecular markers has facilitated fine-scale analysis of populations. However, estimation of SGS may depend strongly on the type of genetic marker and sampling strategy (of both loci and individuals). To explore sampling limits, we created a model population with simulated distributions of dominant and codominant alleles, resulting from natural regeneration with restricted gene flow. SGS estimates from subsamples (simulating collection and analysis with amplified fragment length polymorphism (AFLP) and microsatellite markers) were correlated with the 'real' estimate (from the full model population). For both marker types, sampling ranges were evident, with lower limits below which estimation was poorly correlated and upper limits above which sampling became inefficient. Lower limits (correlation of 0.9) were 100 individuals, 10 loci for microsatellites and 150 individuals, 100 loci for AFLPs. Upper limits were 200 individuals, five loci for microsatellites and 200 individuals, 100 loci for AFLPs. The limits indicated by simulation were compared with data sets from real species. Instances where sampling effort had been either insufficient or inefficient were identified. The model results should form practical boundaries for studies aiming to detect SGS. However, greater sample sizes will be required in cases where SGS is weaker than for our simulated population, for example, in species with effective pollen/seed dispersal mechanisms.

Computer Simulation↗
PubMed2004

Limited pollen dispersal and biparental inbreeding in Symphonia globulifera in French Guiana.

In this paper, we report a study of the mating system and gene flow of Symphonia globulifera, a hermaphroditic, mainly bird-pollinated tree species with a large geographic distribution in the tropical Americas and Africa. Using three microsatellites, we analysed 534 seeds of 28 open pollinated families and 164 adults at the experimental site 'Paracou' in French Guiana. We observed, compared to other tropical tree species, relatively high values for the effective number of alleles. Significant spatial genetic structure was detected, with trees at distances up to 150 m more genetically similar than expected at random. We estimated parameters of the mating system and gene flow by using the mixed mating model and the TwoGener approach. The estimated multilocus outcrossing rate, tm, was 0.920. A significant level of biparental inbreeding and a high proportion of full-sibs were estimated for the 28 seed arrays. We estimated mean pollen dispersal distances between 27 and 53 m according to the dispersal models used. Although the adult population density of S. globulifera in Paracou was relatively high, the joint estimation of pollen dispersal and density of reproductive trees gave effective density estimates of 1.6 and 1.3 trees/ha. The parameters of the mating system and gene flow are discussed in the context of spatial genetic and demographic structures, flowering phenology and pollinator composition and behaviour.

French Guiana↗
PubMed2001

Fine-scale spatial genetic structure of eight tropical tree species as analysed by RAPDs.

The fine-scale spatial genetic structure of eight tropical tree species (Chrysophyllum sanguinolentum, Carapa procera, Dicorynia guianensis, Eperua grandiflora, Moronobea coccinea, Symphonia globulifera, Virola michelii, Vouacapoua americana) was studied in populations that were part of a silvicultural trial in French Guiana. The species analysed have different spatial distribution, sexual system, pollen and seed dispersal agents, flowering phenology and environmental demands. The spatial position of trees and a RAPD data set for each species were combined using a multivariate genetic distance method to estimate spatial genetic structure. A significant spatial genetic structure was found for four of the eight species. In contrast to most observations in temperate forests, where spatial structure is not usually detected at distances greater than 50 m, significant genetic structure was found at distances up to 300 m. The relationships between spatial genetic structure and life history characteristics are discussed.

DNA, Plant↗
PubMed1999

Comparative study of genetic variation and differentiation of two pedunculate oak (Quercus robur) stands using microsatellite and allozyme loci

In a comparative study four codominant microsatellite loci and seven allozyme gene loci have been used to investigate the genetic variation and differentiation of two pedunculate oak stands in North Germany. Both number and effective number of alleles were five to six times higher and the observed heterozygosity was three times higher for the microsatellite than for the allozyme loci. One stand showed an overall excess of homozygotes. In general the microsatellites were closer to Hardy-Weinberg expectation. The genetic distances between the two stands were distinctly higher for microsatellites. For most parameters microsatellites exhibited smaller interlocus variation than the allozymes. The different impact of population genetic processes on the genetic structure as assessed by microsatellites or allozymes is discussed.

Journal Article↗
PubMed1995

Potential of autologous immunologic effector cells for bone marrow purging in patients with chronic myeloid leukemia.

Relapse is a major concern in autologous bone marrow transplantation (BMT). Therefore, purging of bone marrow to reduce the amount of tumor cells reinfused into the patient is widely used. Immunologic effector cells such as lymphokine activated killer (LAK) cells are attractive for purging of bone marrow since these cells might have an additional in vivo effect on tumor cells in contrast to other purging protocols. In patients with chronic myelogenous leukemia (CML), LAK cells can only be used in some patients for purging bone marrow since LAK cells possess no or only limited cytolytic activity against autologous CML tumor cells in most cases. In this study, we investigated the effect of autologous and allogeneic cytokine-induced killer (CIK) cells on tumor cells from patients with CML. CIK cells have been generated from peripheral blood lymphocytes by incubation with interferon-gamma on day 0, interleukin-1, interleukin-2 and a monoclonal antibody against CD3 on day 1. In contrast to LAK cells, CIK cells were able to lyse both autologous and allogeneic cells from patients with CML as determined by a 51Cr release and a tumor colony assay. The cytotoxicity of CIK cells against CML cells was confined to the CD56+ population. CIK cells showed no major toxic effect on hematopoietic progenitor cells when tested in CFU-GM assays. CIK cells eliminated three orders of magnitude of K562 cells and less than one order of magnitude of progenitor cells (25% reduction). This represents a differential effect of CIK cells on tumor and progenitor cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1983

[Prenatal diagnoses in a family with pericentric inversion of chromosome no. 5].

A hereditary pericentric inversion of chromosome 5(p13 leads to q35) was detected in a family after the birth of a child with Cri-du-Chat-syndrome [46,XY,del(5)(p13)]. Prenatal diagnoses were carried out in three pregnancies in this family. The following results were found in the amniotic fluid cells: first pregnancy 46,XX; second 46,XY, inv(5)(p13 leads to q35) and the third 46,XX,der (5)(pter leads to q35::p13 leads to pter). The first two pregnancies ended with the birth of phenotypically normal children; the third one however was interrupted. Fetal kidney tissue cultures confirmed the result of the amniotic fluid cell culture.

Adult↗
PubMed1977

[Effect of temperature on the transcription of T3 DNA b y T3-specific RNA polymerase in cell-free extracts of Escherichia coli CRT266].

Cell free extracts were prepared from E. coli CRT266 9 min after infection with T3 phages. RNA synthesis in these extracts is almost entirely due to T3 RNA polymerase. The inactivation of T3 RNA polymerase in these extracts proceeds rapidly at 42 degrees C. 90% of the activity is lost within 10 min at this temperature. Under conditions where the formation of a stable initiation complex with T3 DNA is possible, i.e., in the presence of GPT, APT, and UTP the T3 RNA polymerase becomes protected against heat inactivation losing only )0% of its activity during an exposure to 42 degrees C for 10 min. Studies on the time course of RNA synthesis have shown that reinitiation is still possible at 37 degrees C and 42 degrees C. At 44 degrees C, however, RNA synthesis stops abruptly after 3 min indicating that reinitiation does no longer take place. The elongation of already initiated T3 RNA chains is rather resistant to heat. At 44 degrees C the same elongation rates are observed as at 37 degrees C and 42 degrees C, respectively.

Cell-Free System↗
PubMedDate not supplied

[Multiplication of chromosomes and primary leucocyte number in childhood ALL and hyperdiploid karyotype].

In the blast cells of children with acute lymphoblastic leukemia (ALL) more than 50 chromosomes can be observed in a quarter of cases. As a rule these children have a good prognosis. However, some of these patients develop a relapse of their basic disease. There is only poor information about the significance of distinct additional chromosomes for the prognosis. The white blood cell count (WBC) at the time of diagnosis is a further very important prognostic factor in childhood ALL. Therefore we compared the relation between trisomy of distinct chromosomes and the initial white blood cell count of 41 children with common ALL and hyperdiploid karyotype. The modal chromosome number ranged from 50 to 60 chromosomes. Most frequently, the chromosomes X, 4, 6, 8, 10, 17, 18 and 21 were multiplied. Additionally, in 25 of the 41 cases structural chromosome aberrations were observed. The average WBC was estimated as 9.6 Gpt/l with a range from 1.8 to 41.5 Gpt/l. The initial WBC was slightly increased in patients with the additional chromosome X, 6, 11, 12 or 19 and distinctly decreased in children with the additional chromosome 8 or 9 in their hyperdiploid blast cells. No patient with an additional Chromosome 9 showed a WBC higher than 10 Gpt/l and only 2 out of the 12 children with an additional chromosome 8 revealed an initial WBC higher than 10 Gpt/l. Additional structural chromosome aberrations were without influence on the WBC.

Adolescent↗
PubMedDate not supplied

SGS--Spatial Genetic Software: a computer program for analysis of spatial genetic and phenotypic structures of individuals and populations.

We have developed a program called Spatial Genetic Software (SGS), which provides a user-friendly Windows tool to analyze both local and broad scale genetic and phenotypic structure. It can deal with nearly any type of genetic data, codominant (allozyme, PCR-RFLP, microsatellite) or dominant (RAPD, AFLP) markers, or biparentally (nuclear) or uniparentally (cpDNA and mtDNA) inherited markers. Data based on any of these markers can be analyzed, either as individual genotypes within a single population (local scale) or as allele or haplotype frequencies from different populations (broad scale). We also include a simple approach to analysis of spatial structure for continuous quantitative traits. The program implements various parameters to analyze spatial genetic and phenotypic structure: Moran's index, Geary's index, number of alleles in common, and approaches using genetic distances and F(ST) values. The statistical significance of all measures is verified by the use of a permutation test. The results are assessed by graphics that can be integrated, via the clipboard, to other Windows programs. The details of the computations are given in a table and can be stored as ASCII files.

Demography↗