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PubMed2000

How can we distinguish between mutational "hot spots" and "old sites" in human mtDNA samples?

New research into variation in mutation rates across nucleotide positions in human mitochondrial DNA (mtDNA) calls into question population genetics models that assume a constant mutation rate for all sites in a sequence, particularly for hypervariable control region segments I and II. Related to this research is discovering the extent to which highly polymorphic sites are really mutational "hot spots" rather than "old" sites rooted early in the phylogenetic tree. This issue is addressed through the analysis of linkage disequilibrium patterns in the mtDNAs of 10 human populations. Hot spots can be expected to show little or no disequilibrium since they can be interpreted as having randomly expressed patterns. In fact, the results suggest that many highly polymorphic sites are not old sites, but instead are hot spots. Suspected hot spots are listed and compared with hypervariable sites given by Wakeley (1993) and Hasegawa et al. (1993).

Asia↗
PubMed2001

Studies of the inheritance of seed qualities and the exploitation of F2 heterosis in low gossypol strains in upland cotton.

Twenty cross combinations were made with 4 recessive glandless lines (gl2gl2 gl3gl3) used as females and 5 dominant glandless lines (Gl2eGl2e Gl3Gl3) used as male parents to estimate the genetic variance components of kernel oil and protein content of seeds, oil and protein index, and kernel index using a genetic model for parents, F2 and F3. The results showed that all the analyzed traits were mainly controlled by additive effects. Oil content was controlled mainly by maternal additive effect, and other traits by direct additive effect. The average heterosis of F2 over mid-parent based on population mean was -1.99% to 1.11% for all these traits. It suggests that little inbreeding depression exists for F2 and F3 seeds. There were 75% and 60% of the F2 and the F3 combinations in which open-pollinated seeds contained gossypol levels lower than 0.4 gkg-1. This result indicated that it is possible to screen and select high yielding F2 hybrids with a gossypol content lower than the regulated criterion and without lowering seed quality.

Genotype↗
PubMed2001

Successful production of offspring after superovulation and in vitro culture of embryos from domestic ferrets (Mustela putorius furos).

In an effort to expand the use of ferrets as models for genetic disease, several experimental parameters that are required for successful genetic manipulation in this species were investigated. Optimum superovulation (19.3 +/- 0.6 oocytes and embryos per female) was achieved after injections of 100 iu equine chorionic gonadotrophin (eCG) and 150 iu human chorionic gonadotrophin (hCG). The ovulation rate achieved by the treatment was more than double that induced by mating. Mating with a male immediately after hCG treatment did not significantly alter the number of oocytes ovulated or the number of embryos present, indicating that mating is not required for superovulation in ferrets. Of embryos harvested at the one-cell stage, 64.5% and 47.1% developed into blastocysts when cultured in vitro in CZB or TCM-199 plus 10% fetal bovine serum (FBS) media, respectively. In contrast, only 17.1% of embryos cultured in vitro in NCSU-23 developed to the blastocyst stage. Both freshly retrieved and in vitro cultured embryos from cinnamon-coloured parents produced live young when transferred at the eight-cell stage into albino, pseudo-pregnant recipients. The percentage of kits delivered relative to embryos transferred was 61% for freshly retrieved embryos and 32% for embryos cultured in vitro. These results demonstrate successful embryo transfer in ferrets and provide a basis for further study of genetic modelling approaches in this species after embryo manipulation.

Analysis of Variance↗
PubMed2004

Ethylene signal transduction in Arabidopsis.

It has been more than a centaury since the identification of ethylene as a gaseous plant hormone, and the effects of ethylene on plants have enabled broad applications in agriculture. Efforts had been made to understand ethylene signal transduction in plants, but it had not been successful until the identification and cloning of the first plant hormone receptor gene, ETR1, in Arabidopsis a decade ago. Comprehensive genetic studies allow the dissecting of the signaling pathway to reveal the components involved, which makes the studies of ethylene signal transduction become one the most-understood signal transduction pathways in plants. The identification of the signaling components and the genetic model of ethylene signal transduction pathway are described in this review.

Arabidopsis↗
PubMed1992

Genetic alterations underlying colorectal tumorigenesis.

Colorectal tumours have proven to be an excellent system in which to identify and study the genetic alterations involved in the development of a common human neoplasm. A prevalent view is that colorectal tumours appear to arise as the result of multiple genetic alterations in the alleles of both oncogenes and tumour suppressor genes. The accumulation of genetic alterations appears to accompany the clinical and biological progression of the tumours and may determine the phenotype of the tumour cells. In addition to the many somatic alterations identified at various stages of colorectal tumour development, recent studies have led to the identification of the adenomatous polyposis coli (APC) gene, which, when mutated in the germline, predisposes to the development of colorectal tumours. On the basis of studies of inherited and somatic mutations in colorectal tumours, a genetic model for colorectal cancer development has been proposed. Although the model is undoubtedly incomplete, it nevertheless provides a useful framework for further studies of the multiple events that underlie human tumour initiation and progression. Numerous questions remain to be answered, including identification of the normal function of the genes implicated in tumorigenesis, how mutations in these genes arise and are selected for and what the relative contribution of the altered genes is to various stages of the neoplastic process. Nevertheless, an optimistic outlook is that fundamental insights into the pathogenesis of human cancer are within our reach.

Chromosome Deletion↗
PubMed1990

Application of DNA fingerprints for cell-line individualization.

DNA fingerprints of 46 human cell lines were derived using minisatellite probes for hypervariable genetic loci. The incidence of 121 HaeIII DNA fragments among 33 cell lines derived from unrelated individuals was used to estimate allelic and genotypic frequencies for each fragment and for composite individual DNA fingerprints. We present a quantitative estimate of the extent of genetic difference between individuals, an estimate based on the percentage of restriction fragments at which they differ. The average percent difference (APD) among pairwise combinations from the population of 33 unrelated cell lines was 76.9%, compared with the APD in band sharing among cell lines derived from the same individual (less than or equal to 1.2%). Included in this survey were nine additional cell lines previously implicated as HeLa cell derivatives, and these lines were clearly confirmed as such by DNA fingerprints (APD less than or equal to 0.6%). On the basis of fragment frequencies in the tested cell line population, a simple genetic model was developed to estimate the frequencies of each DNA fingerprint in the population. The median incidence was 2.9 X 10(-17), and the range was 2.4 X 10(-21) to 6.6 X 10(-15). This value approximates the probability that a second cell line selected at random from unrelated individuals will match a given DNA fingerprint. Related calculations address the chance that any two DNA fingerprints would be identical among a large group of cell lines. This estimate is still very slight; for example, the chance of two or more common DNA fingerprints among 1 million distinct individuals is less than .001. The procedure provides a straightforward, easily interpreted, and statistically robust method for identification and individualization of human cells.

Alleles↗
PubMed1987

Complex segregation analysis of febrile convulsions.

Complex segregation analysis was performed on 467 nuclear families ascertained through febrile-convulsion probands. The probands were identified as having their first febrile convulsion while residents of Rochester, MN, during the years 1935-64. Parents and first- and second-degree relatives of probands were identified through the Olmsted County, MN, record-linkage system. Diagnoses of convulsive activity were made from review of medical records. The genetic models investigated included both single-major-locus and polygenic models, with likelihoods computed jointly on children and parents as well as being conditioned on parental phenotype. Possible heterogeneity was investigated by means of analyses of frequency of febrile convulsions in the proband. Analyses of the entire data set indicated that the single-major-locus models could be rejected. The most parsimonious model for these data was the pure polygenic (or common familial environment) model with a large heritable component (68% +/- 7%). However, when families were partitioned on the basis of frequency of febrile convulsions in the proband, significant heterogeneity was present. Our results indicated that the polygenic model was strongly corroborated in families of probands with a single febrile convulsion. In families of probands with multiple febrile convulsions, evidence was consistent with a single-major-locus model with nearly dominant seizure susceptibility.

Child, Preschool↗
PubMed1986

Genetic analysis of plasma sitosterol, apoprotein B, and lipoproteins in a large Amish pedigree with sitosterolemia.

We previously reported the finding of phytosterolemia, xanthomatosis, and hyperapobetalipoproteinemia (hyperapoB) in five siblings in a large Amish pedigree ascertained through a 13-year-old boy who died suddenly from advanced coronary atherosclerosis. Here, we present further analyses of the plasma levels of the plant sterol, sitosterol, of low density (beta) lipoprotein (LDL) sterol, and of LDL B protein. Of 254 relatives and spouses of the proband, 90.5% were examined. A series of genetic models were explored using a pedigree analysis where parameters reflecting frequency, transmission, and penetrance of putative genotypes were examined simultaneously using a maximum likelihood approach. Segregation analysis of the sitosterol levels showed that the phenotype of sitosterolemia was controlled by a rare autosomal recessive gene. There was also significant familial correlation in plasma sitosterol levels that was attributed to a polygenic component under a mixed model but could also be due to shared environments such as diets. The recessive model was supported by our finding that the plasma sitosterol levels in the parents and in six children born to three of the five sitosterolemics were less than 1 mg/dl, well within the normal range. The phenotype of hyperapoB is based on an elevated level of LDL B protein in the presence of a normal LDL cholesterol level (low LDL sterol to LDL B ratio). For both LDL sterol and LDL B, a polygenic model showed a slightly greater improvement in ln likelihood than did the Mendelian single locus model when both were compared to a sporadic model. Similar results were obtained for sterol levels of high density (alpha) lipoprotein (HDL) sterol. When segregation analysis was performed using the ratio of LDL sterol to LDL B, the Mendelian single locus model gave a slightly better fit to the data than did the polygenic model. While the analyses presented here provided unequivocal evidence for the recessive phenotype of phytosterolemia, we also identified a possible single gene factor that could account for the major portion of the strong familial aggregation in the ratio of LDL sterol to LDL B, and to a lesser extent LDL B. However, there is clear evidence of familial aggregation for these traits in this pedigree beyond that due to Mendelian components.

Adolescent↗
PubMed1984

[Role of the genes in odontogenesis].

The authors suggest a genetic model of dental development. This model is based on chromosomal mapping of genes involved in odontogenesis. The role of X and Y chromosomes is updated.

Chromosome Aberrations↗
PubMed1982

H-deficient blood groups ( Bombay) of Reunion Island.

Forty-two H-deficient individuals (lacking H antigen on erythrocytes) with anti-H in their sera were found on Reunion Island. A, B, and AB Bombay subjects had small but detectable amounts of A and/or B antigens on erythrocytes. All the H-deficient phenotypes tested were nonsecretors of ABH in their saliva, and one-third were Lewis negative. Fifty-three of the 108 (49%) unaffected members in the 14 Bombay pedigrees analyzed were se/se, showing that the families were selected for the nonsecretor trait, and suggesting that the Bombay probands used to select the families have se/se genotype. In accordance with this concept, all the children from Bombay nonsecretor x unaffected nonsecretor matings were se/se. Segregation of H and Se is compatible with the genetic model proposing that Se and H are closely linked structural genes, and the analysis of the present and previously published Bombay pedigrees strongly supports this model.

ABO Blood-Group System↗
PubMed1981

Optimal sampling for pedigree analysis: relatives of affected probands.

Criteria and rules are derived for the most statistically efficient sampling of relatives of affected probands under a simple class of standard genetic models. Results show that the optimal relative type depends on the alternative hypotheses of particular interest. Thus, there is no uniformly optimal strategy, but the criteria can be used to derive the best strategy in any particular case; examples are given.

Female↗
PubMed1993

Lung structure and elastic recoil properties in hereditary diabetes mellitus in KK-mice, C57 black mice, and F1 hybrids.

To separate the effects of diabetes and inheritance on morphometric characteristics of the lung and on the variables of the pressure-volume relationship, the lungs of KK mice--a genetic model of adult-onset diabetes--were compared with the lungs of normal C57 black mice and of F1 hybrids by multivariate analysis. Hybrid mouse lungs contain more air per gram of lung tissue at total lung capacity (TLC) than the lungs of other mice (p < 0.0002) and have a lower recoil pressure at 30% to 70% of TLC. Morphometric data revealed that both the mean linear intercept and the number of alveoli per unit volume in hybrid mice fell between those in KK and C57 mice. However, the total number of alveoli per lung in hybrid mice was 155% of that in KK mice and 148% of that in C57 mice, reflecting the larger lung volume of hybrid mice. The alveolar wall thickness of the hybrids was similar to that of C57 mice, whereas KK mice had thicker alveolar walls than the other two groups. Multivariate analysis revealed that body weight, wet lung weight, volume density of blood vessels, mean linear intercept, and transpulmonary pressure at 90% TLC were affected by diabetes alone; however, the following parameters were affected by both inheritance and diabetes: lung volume, specific lung volume, femur length, volume density of alveolar air, surface area, surface to volume ratio, number of alveoli per lung, lung air per gram of lung tissue, and transpulmonary pressure at 20% to 80% TLC.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

The M-N--V-A-B-D blood group system of chimpanzee and other apes: serology and genetics.

Poly- and monoclonal anti-M and anti-N reagents detect on the red cells of anthropoid apes the M and/or N antigens which are similar to, but not identical with human M and N. A series of V-A-B-D specificities, closely related to the M-N system, are recognized on ape red blood cells by chimpanzee immune sera. To account for the distributions of the M-N--V-A-B-D types in man and in various apes, a genetic model is proposed that assumes the existence of two independent pairs of alleles: M/m, and N/n. In the processes of speciation, some of the alleles were lost or replaced by multiple mutations, resulting in chimpanzee in a series of codominant alleles responsible for as many as 16 M-N--V-A-B-D phenotypes.

Alleles↗
PubMed1995

The search for genetic mechanisms of congenital heart disease.

Identification of the genetic basis for congenital heart defects has been a topic of inquiry for pediatric cardiologists for many years. Any genetic model proposed must account for three often puzzling features of congenital heart diseases, namely the high population incidence, the less than Mendelian recurrence risk, and low concordance rates of heart lesions within individual families. A multifactorial or polygenic inheritance model has been used to explain these observations. Although this model has been serviceable, it does not adequately explain the phenotypic variability within families. Further, the emphasis on teratogenic influences has not led to the elucidation of pathogenetic mechanisms. The multifactorial model should be modified to include the role of chance as originally proposed by Kurnit. Once the role of chance is acknowledged, the phenotypic variability of congenital heart diseases becomes less problematic, and the multifactorial model gives way to a model in which single genes are capable of producing congenital heart disease. Through recent work in animal models and humans, it is now clear that single congenital heart disease genes can be identified that produce phenotypic variability in families that is similar to that seen in the population as a whole. Examples demonstrating recent progress in the search for major congenital heart disease genes are discussed.

Animals↗
PubMed1997

Prevalence and contribution of BRCA1 mutations in breast cancer and ovarian cancer: results from three U.S. population-based case-control studies of ovarian cancer.

We investigate the familial risks of cancers of the breast and ovary, using data pooled from three population-based case-control studies of ovarian cancer that were conducted in the United States. We base estimates of the frequency of mutations of BRCA1 (and possibly other genes) on the reported occurrence of breast cancer and ovarian cancer in the mothers and sisters of 922 women with incident ovarian cancer (cases) and in 922 women with no history of ovarian cancer (controls). Segregation analysis and goodness-of-fit testing of genetic models suggest that rare mutations (frequency .0014; 95% confidence interval .0002-.011) account for all the observed aggregation of breast cancer and ovarian cancer in these families. The estimated risk of breast cancer by age 80 years is 73.5% in mutation carriers and 6.8% in noncarriers. The corresponding estimates for ovarian cancer are 27.8% in carriers and 1.8% in noncarriers. For cancer risk in carriers, these estimates are lower than those obtained from families selected for high cancer prevalence. The estimated proportion of all U.S. cancer diagnoses, by age 80 years, that are due to germ-line BRCA1 mutations is 3.0% for breast cancer and 4.4% for ovarian cancer. Aggregation of breast cancer and ovarian cancer was less evident in the families of 169 cases with borderline ovarian cancers than in the families of cases with invasive cancers. Familial aggregation did not differ by the ethnicity of the probands, although the number of non-White and Hispanic cases (N = 99) was sparse.

Adult↗
PubMedDate not supplied

[Dynamic DNA mutations, anticipation and schizophrenia].

Recently, a new form of human mutation-expansion of trinucleotide repeats-has been found to cause fragile X syndrome, Huntington's disease and other neurodegenerative diseases. These diseases are characterized by unusual patterns of inheritance, in particular, genetic anticipation in which the severity of the disorder increases and the age at onset decreases in successive generations of a pedigree. This phenomenon, formerly ascribed to observation biases, correlates with the expansion of trinucleotide repeat sequences. Two recent studies indicate that anticipation is present in familial schizophrenia. These findings support both an active search for unstable trinucleotide repeat sequences in schizophrenia and reconsideration of the genetic models used in this disorder.

Adolescent↗
PubMed1998

Segregation analysis in nonsyndromic holoprosencephaly.

Holoprosencephaly (HPE) is a developmental defect due to a failure of cleavage of the forebrain. The brain malformations are usually associated with facial anomalies. From a series of 258 HPE records involving at least one affected child, 97 cases in 79 families with nonsyndromic and nonchromosomal HPE were selected. The male:female ratio was 0.87. A high degree of familial aggregation was observed in 23/79 families (29%). A segregation analysis performed in the 79 nuclear families led to the conclusion that the transmission of nonsyndromic HPE is compatible with an autosomal dominant mode of inheritance. Under this hypothesis, the penetrance was estimated as 82% for major types (alobar, semilobar, lobar) and 88% when major and minor types (atypical) were included. The proportion of sporadic cases was estimated to be 68%. This genetic model allows a prediction of the recurrence risk after an isolated case of 13% for major types and 14% when minor types are included.

Diseases in Twins↗