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At least 1,171 records · Page 65Linked to original sources
PubMed1974

The genetics of Caenorhabditis elegans.

Methods are described for the isolation, complementation and mapping of mutants of Caenorhabditis elegans, a small free-living nematode worm. About 300 EMS-induced mutants affecting behavior and morphology have been characterized and about one hundred genes have been defined. Mutations in 77 of these alter the movement of the animal. Estimates of the induced mutation frequency of both the visible mutants and X chromosome lethals suggests that, just as in Drosophila, the genetic units in C. elegans are large.

Animals↗
PubMed1975

Mitotic chromosome loss in a disomic haploid of Saccharomyces cerevisiae.

Experiments designed to characterize the incidence of mitotic chromosome loss in a yeast disomic haploid were performed; The selective methods employed utulize the non-mating property of strains disomic for linkage group III and heterozygous at the mating type locus. The principal findings are: (1) The grequency of spontaneous chromosome loss in the disome is of the order 10- minus 4 per cell; this value approximates the frequency in the same population of spontaneous mitotic exchange resulting in homozygosity at the mating type locus. (2) The recovered diploids are pure clones, and thus represent unique events in the disomic haploid. (3) Of the euploid chromosomes recovered after events leading to chromosome loss, approximately 90% retain the parental marker configuration expected from segregation alone; however, the remainder are recombinant for marker genes, and are the result of mitotic exchanges in the disome, especially in regions near the centromere. The recombinant proportion significantly exceeds that expected if chromosome loss and mitotic exchange in the disome were independent events. The data are consistent with a model proposing mitotic nondisjunction as the event responsible for chromosome loss in the disomic haploid.

Chromosome Mapping↗
PubMed1981

Studies of esterase 6 in Drosophila melanogaster. VI. ejaculate competitive abilities of males having null or active alleles.

Recent studies of the function of the polymorphic seminal fluid enzyme, esterase 6, of Drosophila melanogaster suggested that it may act in the process of sperm displacement (Gilbert, Richmond and Sheehan, 1981a). This report examines the competitive ability of ejaculates from males homozygous for null or active alleles of esterase 6 under three experimental conditions that model aspects of sexual selection affecting males. The results demonstrate no significant difference in ejaculate competition between esterase 6 null or active male types, but marker males used for paternity identification had poorly competitive ejaculates. The proportion of second-male progeny, P2, used as an index of competition is primarily influenced by second-male genotype and uninfluenced by female genotype, P2 can change with time from remating and be unaffected by different intensities of competition, which suggests a complex ejaculate competition mechanism.

Animals↗
PubMed2000

Avoiding multiple pregnancies in ART: multiple pregnancies: a test case for the moral quality of medically assisted reproduction.

Although most professional societies have issued guidelines to diminish the number of embryos to be transferred during assisted reproduction techniques, the incidence of multiple pregnancies remains unacceptably high. The negative psychological, social and medical consequences for the patients and their offspring easily outweigh the benefits in terms of increased success rates. Multiple pregnancies would never be tolerated if the 'best interest of the child' standard was applied as strictly to these consequences, as it is to controversial family forms. The persistence of high multiple pregnancy rates is largely due to the pressure brought to bear on the physicians to increase the overall success rate. The fertility specialist should inform the patients about the risks and benefits of a multiple transfer but ultimately the specialist should decide how many embryos to transfer. Multifetal reduction is an ethically acceptable solution if, and only if, the physician has taken all reasonable steps to prevent the occurrence of a multiple pregnancy. Finally, an additional strategy to decrease the incidence of multiple pregnancies is proposed, i.e. to extend the professional responsibility of the fertility specialist to all steps of procreation including pregnancy, birth and neonatal care.

Child↗
PubMed2001

ART in HIV-infected couples: has the time come for a change of attitude?

Today, in developed countries, many HIV-infected people remain in good health thanks to antiviral medication. A growing number of them want to have children. Medical possibilities for preventing contamination of the partners of seropositive men, through assisted reproduction, and of children thanks to antiviral medicines during pregnancy, are summarized. These changes result in ethical considerations which lead the authors to question the conventional systematic medical advice against pregnancy and has encouraged them to assist reproduction for a number of these couples. Today, the balance between the importance of the message of prevention and the benefit for patients of being assisted in their desire for a child has tilted towards medical intervention. It would seem legitimate today to intervene in the most favourable situations rather than see these couples take the risk of spontaneous conception outside health care structures. This implies the need to adapt medical structures (separate laboratory, appropriate procedure, precise protocols). This approach, which is coherent from the scientific point of view, respects both the autonomy of people carrying HIV as well as the essential interests of the child, in being born uninfected, and also has the enormous advantage of allowing access to parenthood without destroying the consistency of the message of prevention of sexual contamination.

Attitude of Health Personnel↗
PubMedDate not supplied

Recombination, statistical power, and genetic studies of sexual isolation in Drosophila.

Genetic studies of sexual isolation in Drosophila have generally failed to fully evaluate the effects of their sample size and recombination between markers on their conclusions. In this study we evaluate recombinational distances between markers in Drosophila pseudoobscura and D. persimilis, a species pair in which numerous genetic mapping studies have been performed. We conclude that, contrary to assertions, the inversions that distinguish these two species still allow for much recombination within most of their chromosome arms in F1 hybrid females. Such recombination may have caused previous mapping studies in these species to miss (or grossly underestimate) the effects of several genomic regions. We also evaluate the effects of sample size and recombination on genetic studies of sexual isolation in other Drosophila species groups. We conclude that some of these studies may have been heavily biased toward detecting only genes of large effect. Future studies of sexual isolation should be preceded by detailed statistical power analyses that determine the effects of recombination and sample size in the species pair being studied to avoid these complications.

Animals↗
PubMedDate not supplied

A new search for restorer cytoplasm: the restorer cytoplasm for the gene ms10 most probably does not exist in maize.

Since the suggestion concerning the hypothesis of the existence of restorer cytoplasms for some of the known and currently available male sterile (ms) genes in maize, a relatively limited amount of research effort has been made in order to test the hypothesis. Considering the importance of such a phenomenon, we designed a large, two-part experiment to test the idea more seriously. In the first part, 50 randomly chosen, medium-late open-pollinated (OP) varieties of maize from the Zemun Polje (ZP) collection were tested for the presence of the restorer cytoplasm in some currently known ms-genes in maize (ms1, ms2, ms3, ms4, ms5, ms6, ms7, ms8, ms9, ms11, ms12, ms13, ms17, ms22, ms23, and ms24). In the second part, the whole ZP collection of maize germplasm (more than 4,000 entries) was tested for the presence of the restorer cytoplasm for the gene ms10. After the first basic screening of OP varieties, more than 70 nonsegregating "candidates" were identified; however, after additional screening of the collection and the direct testing with respective homozygous ms-testers, all of them showed segregation, indicating that the restorer cytoplasm does not exist, especially the gene ms10. While performing this experiment, we discovered almost a hundred sources of male sterile cytoplasm, which were distinguished by their overwhelming frequency of male sterile plants in segregating test progenies.

Fertility↗
PubMed2004

Independent origins of allotriploidy in the fish genus Poeciliopsis.

We examined mitochondrial DNA (mtDNA) sequences and allozymes to assess possible modes of origin, clonal diversity, and evolutionary age in a triploid all-female fish of the genus Poeciliopsis from the state of Sinaloa, Mexico. Analysis of multilocus allozymes revealed that the Rio Mocorito biotype (Poeciliopsis monacha-lucida-viriosa) is trihybrid, carrying haploid genomes from three sexually reproducing species, Poeciliopsis monacha, Poeciliopsis lucida, and Poeciliopsis viriosa. Composite allozyme and mtDNA genotypes identified four clones, all bearing closely related mitochondrial haplotypes originally derived from P. monacha. Apparently these trihybrids arose endemically by addition of a haploid genome from P. viriosa, a local sexual species, to an allodiploid biotype, P. monacha-lucida, also found in the Rio Mocorito. The present analysis clearly revealed that P. monacha-lucida-viriosa arose independently of the two allotriploid biotypes that live in a river to the north (Rio Fuerte). Although the origins of allotriploidy in Poeciliopsis are less constrained phylogenetically and geographically than previously thought, known triploid biotypes all had relatively recent origins, which supports the notion that most asexual lineages are evolutionarily short-lived.

Aneuploidy↗
PubMed1996

Feminist critiques of new fertility technologies: implications for social policy.

This essay aims to show how feminist theoretical and practical perspective have enriched and deepened debate about moral and social issues generated by the proliferation and commodification of new reproductive techniques. It evaluates alternative feminist appraisals beginning with the first group to organize a collective response to the medicalization of infertility and explores several weaknesses working within their assessment: objectification of infertile women, naturalizing constructions of motherhood, hostility to technology, and an overly simplistic conception of power relations. Next, it shows how subsequent feminists have reframed the issues to overcome these weaknesses, drawing on themes prominent in recent theoretical debates: the need to reclaim women's agency, to revalue mothering, and to reappraise power relations. Lastly, it weighs the prospects for a collaborative politics that is sensitive to the social marginalization of vulnerable women and suggests practical strategies for responding to mounting pressures to procreate at any price.

Dehumanization↗
PubMed1977

Geographic patterns of breast cancer in the United States.

To seek explanations for the geographic variation of breast cancer across the continental United States, we calculated the correlations between mortality rates for premenopausal and postmenopausal women and demographic data for the 3,056 U.S. counties. The northern predominance of this tumor was primarily among postmenopausal women, whereas mortality among premenopausal women was distributed almost uniformly across the country. Socioeconomic status (particularly income), German ethnicity, and colon cancer mortality were strong indicators of the rates for postmenopausal women, but only partly explained the northern excess and latitudinal gradient. In contrast, fertility patterns and ovarian cancer mortality were more closely linked to breast cancer among premenopausal women. The geographic peculiarities of this tumor in older women suggest extrinsic risk factors that remain to be identified, whereas the patterns for younger women point to the primary role of reproductive and genetic determinants.

Adult↗
PubMed2003

Evidence of recombination in putative ancient asexuals.

Ancient asexuals have been considered to be a contradiction of the basic tenets of evolutionary theory. Barred from rearranging genetic variation by recombination, their reduced number of gene arrangements is thought to hamper their response to changing environments. For the same reason, it should be difficult for them to avoid the build-up of deleterious mutations. Several groups of taxonomically diverse organisms are thought to be ancient asexuals, although clear evidence for or against the existence of recombination events is scarce. Several methods have recently been developed for predicting recombination events by analyzing aligned sequences of a given region of DNA that all originate from one species. The methods are based on phylogenetic, substitution, and compatibility analyses. Here we present the results of analyses of sequence data from different loci studied in several groups of evolutionarily distant species that are considered to be ancient asexuals, using seven different types of analysis. The groups of organisms were the arbuscular mycorrhizal fungi (Glomales), Darwinula stevensoni (Darwinuloidea crustacean ostracods) and the bdelloid rotifers (Bdelloidea), which are thought to have been asexual for the last 400, 25-100, and 35-40 Myr, respectively. The seven different analytical methods evaluated the evolutionary relationships among haplotypes, and these methods had previously been shown to be reliable for predicting the occurrence of recombination events. Despite the different degree of genetic variation among the different groups of organisms, at least some evidence for recombination was found in all species groups. In particular, predictions of recombination events in the arbuscular mycorrhizal fungi were frequent. Predictions of recombination were also found for sequence data that have previously been used to infer the absence of recombination in bdelloid rotifers. Although our results have to be taken with some caution because they could signal very ancient recombination events or possibly other genetic variation of nonrecombinant origin, they suggest that some cryptic recombination events may exist in these organisms.

Animals↗
PubMed1996

Cytogenetic effects of caffeine during in vivo mouse oocyte maturation.

Numerous investigators have studied the reproductive and genetic toxicity of caffeine. Caffeine has also been reported to retard meiotic progression and induce aneuploidy in hamster oocytes in vitro. However, the ability of caffeine to induce aneuploidy in mammalian oocytes in vivo has not been reported. The objective of this study was to test the hypothesis that chemical-induced perturbations during in vivo oocyte meiotic maturation (OM) predispose oocytes to chromosome missegregation. Caffeine inhibits cAMP phosphodiesterase, which is needed for dephosphorylating p34(cdc2) kinase and initiating OM. Following superovulation, a dose of 150 mg/kg caffeine was administered to Institute of Cancer Research (ICR) female mice at various times prior to metaphase I (MI). Ovulated oocytes were collected from the oviducts and processed for cytogenetic analysis. Statistical analyses of the frequencies of hyperploid, MI, diploid, premature centromere separation and single chromatids revealed nonsignificant (P > 0.05) differences between the controls and each of the caffeine groups. Structural chromosome aberrations were not found. Under our experimental conditions, we rejected the hypothesis and concluded that caffeine neither retarded the rate of OM nor increased the incidence of aneuploidy in mouse oocytes. The factors responsible for the different in vivo and in vitro responses require investigation.

Aneuploidy↗
PubMed1986

A family of DNA sequences is reproducibly rearranged in the somatic nucleus of Tetrahymena.

A small family of DNA sequences is rearranged during the development of the somatic nucleus in Tetrahymena. The family is defined by 266 bp of highly conserved sequence which restriction mapping, hybridization and sequence analysis have shown is shared by a cloned micronuclear fragment and three sequences which constitute the macronuclear family. Genomic Southern hybridization experiments indicate there are five members of the family in micronuclear DNA. All of the family members are present in whole genome homozygotes and are therefore nonallelic. The three macronuclear sequences are all present in clonal cell lines and are reproducibly generated in every developing macronucleus. The rearrangement event begins 14 hours after conjugation is initiated and is nearly completed by 16 hours.

Animals↗
PubMed1994

RNA editing of transcripts of a chimeric mitochondrial gene associated with cytoplasmic male-sterility in Brassica.

The orf224 gene is a chimeric open reading frame associated with the Polima or pol cytoplasmic male sterility of Brassica napus. The first 58 codons and 5' upstream region of orf224 are derived from a conventional mitochondrial gene, orfB, while the origin of the remaining portion of the gene is unknown. Transcripts of the orf224 gene were found to be edited at a single site in the region of the gene that does not correspond to a known sequence. Oligonucleotides corresponding to the edited and unedited forms were shown to hybridize specifically to respective in vitro orf224 transcripts. Analysis of floral mtRNA by this method indicated that virtually all orf224 transcripts of both sterile and fertile, nuclear-restored pol cytoplasm plants are edited. Our results indicate that transcripts of novel, CMS-associated genes may be edited, but that, at least in this case, the degree of editing does not appear to be directly related to the male-sterile phenotype.

Amino Acid Sequence↗