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PubMed2000

Bias correction for segregation ratio estimation in human genetics.

Segregation ratio estimation has long been important in human genetics. A simple truncated binomial model is considered that assumes complete ascertainment and a deterministic genotype-phenotype relationship. A simple but intuitively appealing estimator of the segregation ratio, previously proposed, is shown to have a negative bias. It is also shown that the bias of this estimator can be largely reduced via a randomization device, resulting in a new estimator that has the same large-sample behavior but with a negligible bias (decaying at a geometric rate). Numerical results are given to show the small-sample performance of this new estimator. An extension to incomplete ascertainment is also considered.

Biometry↗

PubMed2005

Genetic segregation of spontaneous erosive arthritis and generalized autoimmune disease in the BXD2 recombinant inbred strain of mice.

The BXD2 strain of mice is one of approximately 80 BXD recombinant inbred (RI) mouse strains derived from an intercross between C57BL/6J (B6) and DBA/2J (D2) strains. We have discovered that adult BXD2 mice spontaneously develop generalized autoimmune disease, including glomerulonephritis (GN), increased serum titres of rheumatoid factor (RF) and anti-DNA antibody, and a spontaneous erosive arthritis characterized by mononuclear cell infiltration, synovial hyperplasia, and bone and cartilage erosion. The features of lupus and arthritis developed by the BXD2 mice segregate in F2 mice generated by crossing BXD2 mice with the parental B6 and D2 strains. Genetic linkage analysis of the serum levels of anti-DNA and RF by using the BXD RI strains shows that the serum titers of anti-DNA and RF were influenced by a genetic locus on mouse chromosome (Chr) 2 near the marker D2Mit412 (78 cm, 163 Mb) and on Chr 4 near D4Mit146 (53.6 cm, 109 Mb), respectively. Both loci are close to the B-cell hyperactivity, lupus or GN susceptibility loci that have been identified previously. The results of our study suggest that the BXD2 strain of mice is a novel model for complex autoimmune disease that will be useful in identifying the mechanisms critical for the immunopathogenesis and genetic segregation of lupus and erosive arthritis.

Albuminuria↗

PubMed1989

Random segregation of DNA strands in epidermal basal cells.

According to the hypothesis proposed by Cairns, stem cells retain the older of the two parental DNA strands, whereas differentiating daughter cells receive the newly synthesized strand, so that a set of "immortal strands" persists in stem cells through successive cell divisions. To test this hypothesis, five successive divisions were induced in basal epidermal cells in vivo by two injections of cholera toxin into mouse skin and cells labeled with [3H]thymidine at the first cell cycle were chased for 50 days. If selective segregation occurs, the labeled strand should be transferred into a non-stem daughter cell after the second division and labeled cells would eventually be eliminated from the epidermis. However, the results suggest random segregation of DNA strands in epidermal basal cells. Labeled basal cells were persistently present throughout the whole epidermis for 50 days. Furthermore, labeled mitotic cells were found after the third division and their numbers of grains decreased exponentially through 5 cycles of divisions.

Animals↗

PubMed2004

Meiotic segregation of translocations during male gametogenesis.

Balanced reciprocal and Robertsonian translocations are the most common structural chromosomal abnormalities in humans. Generally, they are without consequence for the carrier, but for various degrees of oligoasthenoteratozoospermia in men. As these carriers can produce a significant percentage of gametes with an unbalanced combination of the parental rearrangement, there is a more or less significant risk, according to cases, of chromosomal imbalances for their offspring. Therefore, techniques were developed to study the meiotic segregation of these translocations in males. Direct investigation of human sperm chromosomes became possible by karyotyping spermatozoa after penetration of zona-free hamster oocytes and, more recently, using fluorescent in situ hybridization (FISH). This paper reviews the results obtained using these techniques in Robertsonian and reciprocal translocations. The studies on spermatozoa from translocation carriers help the comprehension of the mechanisms of the meiotic segregation. They should be integrated in the genetic exploration of the infertile men, in order to give them a personalized risk assessment of unbalanced spermatozoa, specially as a correlation was found recently between the percentage of abnormal spermatozoa and that of abnormal embryos.

Humans↗

PubMed1990

Mechanism of post-segregational killing by the hok/sok system of plasmid R1: sok antisense RNA regulates formation of a hok mRNA species correlated with killing of plasmid-free cells.

The hok/sok system of plasmid R1, which mediates plasmid stabilization via killing of plasmid-free segregants, encodes two genes: hok and sok. The hok gene product is a potent cell-killing protein. The expression of hok is regulated post-transcriptionally by the sok gene-encoded repressor, an antisense RNA complementary to the hok mRNA leader region. We show here that the hok mRNA is very stable, while the sok RNA decays rapidly. We also observe a new hok mRNA species which is 70 nucleotides shorter in the 3'-end than the full-length hok transcript. The appearance of the truncated hok mRNA was found to be regulated by the sok antisense RNA. Furthermore, the presence of the truncated hok mRNA was found to be correlated with efficient expression of the Hok protein. On the basis of these findings, we propose an extended model in order to explain the killing of plasmid-free segregants by the hok/sok system.

Base Sequence↗

PubMed1992

spbA locus ensures the segregational stability of pTH1030, a novel type of gram-positive replicon.

The replication region of the plasmid pHT1030 of Bacillus thuringiensis was previously mapped to a 2.9 kb DNA fragment. The DNA sequence was analysed and it was shown that the minimal replicon resides within a 1 kb fragment of DNA carrying no potential protein coding sequence. Moreover, no production of single-stranded DNA intermediates was detected in the plasmid-containing cells. pHT1030 therefore belongs to a class of replicons not previously described in Gram-positive bacteria. Examination of the segregational stability of deletion derivatives of pHT1030 in bacilli defined two stability regions. One is located within the minimal replicon of pHT1030, whereas the second (spbA) is not required for replication. spbA encodes a 15 kDa protein and ensures the segregational stability of the plasmid. This effect of spbA is particularly highlighted in sporulation. The absence of the spbA locus gives rise to plasmid-free spores at high frequency, whereas the spbA+ plasmids are stably maintained. The stability of the plasmids during sporulation seems to be correlated with an unequal division of the cell by the sporulation septum.

Amino Acid Sequence↗

PubMed1997

Direct evidence for active segregation of oriC regions of the Bacillus subtilis chromosome and co-localization with the SpoOJ partitioning protein.

We have developed methods for labelling regions of the Bacillus subtilis chromosome with the nucleotide analogue 5-bromodeoxyuridine (BrdU) and for subcellular visualization of the labelled DNA. Examination of oriC-labelled chromosomes in outgrowing spores has provided direct evidence for active segregation of sister chromosomes. Co-immunodetection of Spo0J and BrdU-labelled DNA has directly confirmed the expected close association between this chromosome partitioning protein and the oriC region of the chromosome. The results provide further support for the notion that bacterial cells use an active mitotic-like mechanism to segregate their chromosomes.

Bacillus subtilis↗

PubMed2004

The role of Par proteins in the active segregation of the P1 plasmid.

The parS centromere-like site promotes active P1 plasmid segregation in the presence of P1 ParA and ParB proteins. At the modest growth rate used here, time-lapse and still photomicroscopy shows that the plasmid copies are clustered as a focus at the Escherichia coli cell centre. Just before cell division, the focus is actively divided and ejects bidirectionally into opposite halves of the dividing cell. In the absence of the wild-type parS binding protein ParB, a focus was formed, but generally did not go to the cell centre. The randomly placed focus did not divide and was inherited by one daughter cell only. In the absence of ParA, foci formed and frequently fixed to the cell centre. However, they failed to divide or eject and were left at the new cell pole of one cell at division. Thus, ParB appears to be required for recognition of the plasmid and its attachment to the cell centre, and ParA is required for focus division and energetic ejection from the cell centre. The ATPase active site mutation, parAK122E, blocked ejection. Mutant parAM314I ejected weakly, and the daughter foci took two generations to reach a new cell centre. This explains the novel alternation of segregation and missegregation in successive generations seen in time-lapse images of this mutant.

Bacterial Proteins↗

PubMed1977

Independent segregation of two functional markers expressed on the same B-cell subset in the mouse: the Mls determinants and LPS receptors.

Mice of the C3H/Tif strain display a mixed leukocyte reaction (MLR) with all H-2k strains carrying any of the known alleles of the Mls locus. In particular, C3H/Tif is incompatible with the related substrain C3H/HeJ, from which it also differs at the locus responsible for the recognition of lipopolysaccharides (LPS) as B-cell mitogens, and at the Mod-1 locus. Our genetic analysis indicates that the MLR incompatibility between these strains is not H-2-linked and segregates as controlled by a single locus, most probably identical to Mls, for which the C3H/Tif strain expresses a previously unidentified allele, Mlse. Moreover, segregation data show that this locus assorts independently of LPS responsiveness and that neither marker is closely linked to the Mod-1 locus in linkage group II.

Alleles↗

PubMed2004

Two genes encoding Arabidopsis halleri MTP1 metal transport proteins co-segregate with zinc tolerance and account for high MTP1 transcript levels.

The zinc hyperaccumulator plant Arabidopsis halleri is able to naturally accumulate 100-fold higher leaf zinc concentrations when compared with non-accumulator species such as the closely related A. lyrata and A. thaliana, without showing toxicity symptoms. A novel member of the cation diffusion facilitator (CDF) protein family, an A. halleri metal tolerance protein 1 (MTP1), and the homologous A. thaliana Zn transporter (ZAT)/AtMTP1 metal-specifically complement the zinc hypersensitivity of a Saccharomyces cerevisiae zrc1 cot1 mutant strain. A fusion of the AhMTP1 protein to green fluorescent protein (GFP) localizes to the vacuolar membrane of A. thaliana protoplasts. When compared with A. lyrata and A. thaliana, the total MTP1 transcript levels are substantially higher in the leaves and upregulated upon exposure to high zinc concentrations in the roots of A. halleri. The high MTP1 transcript levels in A. halleri can be primarily attributed to two genetically unlinked genomic AhMTP1 gene copies. The two corresponding loci co-segregate with zinc tolerance in the back-cross 1 generation of a cross between the zinc-tolerant species A. halleri and the zinc-sensitive species A. lyrata. In contrast, a third MTP1 gene in the genome of A. halleri generates only minor amounts of MTP1 transcripts and does not co-segregate with zinc tolerance. Our data suggests that zinc tolerance in A. halleri involves an expanded copy number of an ancestral MTP1 gene, encoding functional proteins that mediate the detoxification of zinc in the cell vacuole. At the transcript level, MTP1 gene copies of A. halleri are regulated differentially and in response to changes in zinc supply.

Amino Acid Sequence↗

PubMed1975

Segregation of a t(14q22q) chromosome in a large kindred.

A large kindred is reported in which 21 members are balanced t(14q22q) carriers. The components of the translocation were identified by autoradiography and G-banding. With the exception of the index case, who was retarded, all of the carriers were phenotypically normal. The segregation pattern of the translocation chromosome was determined in two complete generations. All eight of the progeny in one generation were balanced carriers, and the carrier father of this generation may have been homozygous for the t(14q22q) chromosome. Segregation in the next generation was closer to the expected 1:1 ratio of carrier to non-carrier, the ratio being 11:13.

Chromosome Aberrations↗

PubMed1993

Alternate, adjacent 2 and 3:1 meiotic segregation products from a balanced t(13;18) (q12;q11) carrier.

We present a case in which alternate, adjacent 2 and 3:1 meiotic segregations have occurred in the pregnancies of a female carrier of a balanced reciprocal translocation -46,XX,t(13;18) (q12;q11). Products of five conceptions effectively showed trisomy 18q, trisomy 18p or monosomy 18p. This is one of the rare rearrangements which can give rise to a variety of segregation modes including adjacent 2.

Chromosomes, Human, Pair 13↗

PubMed1997

Reciprocal translocation 4;11 with both adjacent-1 segregants viable within a family.

We describe a family carrying a balanced 4;11 translocation in which both adjacent-1 segregants are viable. The proband had an unbalanced karyotype: 46,XY,der(11)t(4;11)(q34.3;q23.1)mat. At 8.5 years of age he showed trigonocephaly, hypertelorism, epicanthal folds, down-slanting palpebral fissures, low-set ears, anteverted nares, down-turned carp-shaped mouth, and bilateral fifth finger clinodactyly. His maternal aunt was also dysmorphic with high-arched palate, short philtrum and mild developmental delay. Her karyotype was 46,XX,der(4)t(4;11)(q34.3;q23.1)pat. Other relatives who likely carried a chromosomally unbalanced segregant were identified from photographs and medical records. We compare the clinical findings in our family with descriptions of other similar karyotypic abnormalities from previous case reports.

Abnormalities, Multiple↗

PubMed1975

W4(4a) and W6(4b) in diverse human populations. Demonstration of their genetic identity in population and segregation studies.

The status of the W4, W6 system as related to the HL-A system was re-evaluated by means of segregation and mating studies in 200 Dutch families with 755 children. Inclusion analyses were performed on the Fifth Workshop human populations and related to a reference analysis on the main file in Leiden. The results of the mating and segregation analyses showed a good fit for W4 and W6 as a genetic system. The inclusion analyses showed a high degree of concordance. Based on those results, and other cited evidence, it was suggested that W4 and W6 may represent the basic substance of the HL-A antigens in the FOUR series.

Adult↗

PubMed1977

Detection of HLA-D clusters and segregation studies using primed LD typing.

By testing a group of PLT cells over a panel of unrelated restimulating cells, the PLT's could be grouped into clusters according to their ability to discriminate antigen(s) in unrelated cells. The PLT clusters broadly correlated with the homozygous typing cell-defined HLA-D clusters represented on the panel. The PLTs grouped together clearly segregate with a particular HLA haplotype when tested in both unrelated families not possessing the sensitizing haplotype and in the family with the sensitizing haplotype. No influence of HLA SD antigens could be observed in PLT restimulation in the segregation studies.

Epitopes↗

PubMed1980

HLA antigen distribution and HLA haplotype segregation in Crohn's disease.

A study of the HLA-A, -B, -C, and -DR antigens in patients with Crohn's disease and controls did not reveal a significant strong association with a particular HLA antigens. A segregation analysis of parental HLA haplotypes in nine families with at least two children suffering from Crohn's disease did not show a significant deviation from the expected Mendelian segregation.

Crohn Disease↗

PubMed1982

Type I Glanzmann's thrombasthenia segregates independently of Ss and Duffy systems and the A, B, C, factor B, C2 and C4 loci of the HLA complex.

Two patients with type I Glanzmann's thrombasthenia and 20 kindred of these patients belonging to 2 families of the Manouches gipsy tribe have been studied. Quantitative measurements of platelet membrane glycoproteins GP IIb and GP IIIa have made it possible to classify the patients into normal, thrombasthenic or carriers of the thrombasthenic abnormality. We have examined several red cell alloantigens and antigens of the major histocompatibility complex. These studies have shown that: 1) type I Glanzmann's thrombasthenia (GP IIb and IIIa abnormality) segregates independently of Ss and Fy systems and the A, B, C, Bf, C2 and C4 loci of the HLA complex; 2) a rare hemolytically inactive C4 variant segregates in these families but is not associated with the GP IIb and IIIa abnormality.

Blood Platelet Disorders↗

PubMed1984

Linkage and segregation analysis of HLA and congenital hypoaldosteronism due to corticosterone methyl-oxydase deficiency type I and type II.

To determine the genetic relations between HLA and deficiencies of steroidogenic enzymes other than 21-hydroxylase, we investigated HLA and congenital hypoaldosteronism in two families with corticosterone methyl-oxidase type 2 (CMO2) and one family with type 1 (CMO1) deficiency, respectively. Apart from a first documentation of HLA in CMO1 deficiency, our results, combined with those reported previously, excluded close linkage of HLA and CMO2 deficiency. However, loose linkage could not be encluded and the segregation of HLA haplotypes in sibships with CMO2 deficiency deviated significantly from random segregation. We suggest that HLA and CMO2 deficiency may not be independent.

Aldosterone↗