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Results for “Genetic Phenomena”

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At least 19 recordsLinked to original sources
PubMed1996

[Genetic phenomena during early cleavage divisions in Drosophila melanogaster].

Published data on the pattern and genetic control of early cleavage divisions in Drosophila melanogaster are summarized. Data on chromosome elimination induced by the mutation paternal loss (pal), elimination of ring and rod chromosomes, and mitotic exchanges in the hyperploid pronucleus in Drosophila suggest a specific structural role of heterochromatic chromosomal regions during early cleavage. Mutations disturbing early cleavage divisions include mutations with effects assigned to different stages of this process. This allows us to suggest the existence of isofunctional proteins involved in mitosis and alternating during early cleavage. In addition, cleavage divisions apparently include a special mechanism preserving primordia of germ tissue from unbalanced nuclei.

Animals↗
PubMed1982

Aging and cancer as genetic phenomena.

Although the most frequently seen forms of cancer and the changes of senescence have in common the fact that they both occur in old age, their mechanisms are thought to be completely different. Because cancer is usually due to avoidable external agents (such as cigarettes, sunlight, peculiarities of diet, and certain particular hazards of the work place), it is considered a preventable disease. Many of the changes of senescence seem to be simply the inevitable corollary of our innate program of development; homo sapiens is designed to become an optimal, maximally viable product in the late teens, at the time of sexual maturity, and the same processes that lead to this optimalization also lead to a diminished fitness in later life. Although we may eventually abolish most sources of cancer, we should not expect to abolish senescence.

Adolescent↗
PubMed1995

Using high-efficiency mouse germline mutagenesis to investigate complex biological phenomena: genetic diseases, behavior, and development.

A valuable approach to investigating a biological process is to study the effect of mutations in the involved genes. By studying a diverse set of such mutations, one can gain important insights into the roles that the given gene product plays in the biological process. Although this approach has long been recognized, the scarcity of mammalian mutations has largely limited such investigations to simple organisms. It has recently been shown that highly efficient mutagenesis of the mouse germline with a random point mutagen can produce mutations that are valuable in several important ways. First, it can produce numerous different types of mutations. Second, it can be used to mutate genes that have yet to be cloned or characterized. Genes that have been marked by mutation can ultimately yield molecular access after mapping to high resolution and cloning from map position. Such new investigative capabilities will ultimately allow one to gain intimate knowledge of the molecular basis of complex biological processes like behavior and development. Third, mutations can be induced that yield animal models of human heritable diseases. Such disease models allow for intensive research into the etiology of the given disease and also permit the facile evaluation of new therapeutic regimens.

Animals↗
PubMed1994

Mitochondrial encephalomyopathies: clinical and molecular analysis.

The classification of mitochondrial encephalomyopathies relied upon clinical, biochemical, and histological features until the discovery of mitochondrial DNA defects in 1988. Since then, an outburst of molecular genetic information has aided our understanding of the pathogenesis and the classification of these heterogeneous disorders. Novel concepts of maternal inheritance, mitochondrial DNA (mtDNA) heteroplasmy, tissue distribution, and threshold have explained many of the clinical characteristics. The discovery of point mutations, large-scale mtDNA deletions, duplications, and autosomally inherited disorders with multiple mtDNA deletions have revealed new genetic phenomena. Despite our rapidly expanding understanding of the molecular genetic defects, many questions remain to be explored to fill the gap in our knowledge of the relationship between genotype and clinical phenotype.

DNA, Mitochondrial↗
PubMed1974

Mitochondrial genetics in Bakers' yeast: a molecular mechanism for recombinational polarity and suppressiveness.

Recombinational polarity and suppressiveness are two well-known but puzzling cytoplasmic genetic phenomena in bakers' yeast, Saccharomyces cerevisiae. Little progress has been made in characterizing the underlying molecular mechanisms of these phenomena. In this paper we describe a molecular model for recombinational polarity that is compatible with the available genetic evidence. The model stresses the role of small deletions and excision/repair processes in otherwise canonical recombinational events. According to the model, both phenomena require recombination and may share mechanistic elements.

Crosses, Genetic↗
PubMed1994

Non-Mendelian transmission in a human developmental disorder: split hand/split foot.

The study of Mendelian disorders that do not meet some Mendelian expectations has led to an increased understanding of such previously obscure genetic phenomena as anticipation. Split hand/split foot (SHSF), a human developmental malformation, demonstrates such distinctive genetic features as reduced penetrance and variable expressivity. In this study, new pedigrees with defined ascertainment confirm the existence of non-Mendelian transmission characterized by the overtransmission of SHSF from affected fathers to sons.

Fathers↗
PubMed2001

Huntington's disease: a review of the literature on prevalence and treatment of neuropsychiatric phenomena.

A review was made of the literature on Huntington's disease, including the clinical neurology, recent advances in pathophysiology and genetic mechanisms and psychopathology. It can be concluded that research on the latter is scarce, although the subject is relevant because of the co-occurrence of psychiatric, neurological and genetic phenomena, which may lead to novel concepts in the understanding of brain function. So far, attempts to provide a comprehensive and pragmatic description of the psychopathology of Huntington's disease have been disappointing, probably due to the limitations of the DSM classification system in this disorder. Future research should focus not only on this classification system, but also on neuropsychological functioning, because of the degenerative nature of the disease. Systematic and controlled studies should be performed on the treatment of psychiatric abnormalities in Huntington's disease before any conclusions can be drawn.

Age Factors↗
PubMed1992

Hereditary conditions in which the loss of heterozygosity may be important.

Somatic mutations are a common event in multicellular organisms and, therefore, have a significant impact on health. They can lead to either heterozygosity or homozygosity. Since the multistep concept of carcinogenesis presupposes that mutations/deletions of several genes are acquired, the identification and location of the critical genes involved in this sequence is attempted either by the observation of cytogenetic or molecular abnormalities in tumorous tissue or by linkage analysis, or both. The retinoblastoma paradigm of loss of heterozygosity with respect to the loss of the only wild-type allele can be applied to familial neoplasias occurring in all organs as they are summarized in this review. The development of homozygosity in non-malignant tissue has not been extensively investigated. However, its study has contributed to the identification of new genetic phenomena such as parental unidisomy and genomic imprinting.

Genetic Diseases, Inborn↗
PubMed1996

Genetics of split hand and split foot. A case study.

Split hand and split foot is an autosomal dominant disorder that displays several genetic phenomena. These include variable expressivity, reduced penetrance, and segregation distortion. Although not fully understood at the molecular level, all are important in determining transmission of the gene thought to be mapped to the long arm of chromosome 7 (7q21.3-q22.1). These phenomena, therefore, have significant implications for inheritance of split hand and split foot and for proper referral for genetic counseling.

Chromosome Aberrations↗
PubMed1970

Environmental and genetical contributions to class difference: a model experiment.

Flies were divided into two groups on the basis of the number of their bristles, and raised under different environmental (temperature) conditions. In each generation, offspring of the two groups were retained in their group or transferred to the other group, depending on the number of their bristles. After nine generations it was found that the genetic component of the intergroup difference was 42 percent; the portion of the intragroup variance that was genetic phenomena.

Animals↗
PubMed1999

Familial adenomatous polyposis: from bedside to bench and vice versa. A tribute to the somatic cell geneticist P. Meera Khan.

Familial adenomatous polyposis (FAP) is characterized by the presence of numerous adenomatous polyps in the colorectum, as well as an autosomal dominant mode of inheritance. This syndrome will inevitably lead to colorectal cancer when left untreated, and it is estimated that 1% of all colorectal cancer cases are due to it. Over the past 20 years molecular genetic studies on FAP patients have laid down the basis for the elucidation of the genetic phenomena that ultimately result in the development of colorectal cancer. Professor P. Meera Khan was one of the leading authorities in the world of molecular genetics of colorectal cancer in general and of FAP in particular. His scientific contributions from the pre-DNA era up to the recent implementation of molecular genetic research in daily clinical practice have helped revolutionize our approach and management of FAP patients and their relatives.

Adenomatous Polyposis Coli↗
PubMed1998

Evaluating the performance of a genetic test using information from previous studies in place of a gold standard.

OBJECTIVES: To evaluate the performance of a diagnostic test, a researcher usually must classify study subjects with respect to (1) whether the test result was positive or negative and (2) whether the test result should have been positive or negative. To classify the subjects in the second manner, the researcher needs to have access to a gold standard (ie, a test that classifies the subjects with 100% accuracy). The authors show here how to evaluate the performance of a diagnostic test that allows researchers to determine whether a disease that is occurring within a family is attributable to one of two newly discovered genes without the use of a gold standard. METHODS: By taking advantage of well-known genetic phenomena and their statistical implications, the behavior of the diagnostic test is mathematically modeled, and its performance with respect to various criteria is shown to be functions of genetic parameters. RESULTS: The performance of the test over a wide range of values of the genetic parameters was evaluated, and cutoff points that would allow the test to perform very well or well with respect to all criteria were found for almost all of the situations examined. CONCLUSIONS: This test can be used effectively under a wide range of conditions. In addition, because the genetic parameters have been estimated in previous studies, the effectiveness of the test for the specific conditions the researcher may need to run the study under can be evaluated before the study is performed.

Breast Neoplasms↗
PubMed1997

[Study on the relationship between primary Sjögren syndrome and HLA-DRbeta gene].

The pathogenesis of primary Sjögren syndrome (PSS) is unclear yet. In order to investigate the role of genetic factor playing in the mechanism of this disorder, we studied the HLA-DR beta gene distributed in 70 patients with PSS and 136 normal subjects by using PCR-SSP technique. The results showed that the gene frequences of HLA-DR3, DR52 and DR2 in patients with PSS were significantly higher than that in normal controls. However, the gene frequencies of HLA-DR5 and DR9 in PSS patients were lower than that in the control group. There were the same genetic phenomena in the siblings of two PSS patients' families. We also found the relationship between HLA-DR52 and the anti-antibodies of SSA or SSB. Our results concluded that the genetic factor is involved in the pathogenesis of primary Sjögren syndrome.

Adult↗