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At least 325 records · Page 18Linked to original sources
PubMed2005

HLA-G in human reproduction: aspects of genetics, function and pregnancy complications.

The non-classical human leukocyte antigen (HLA) class Ib genes, HLA-E, -G and -F, are located on chromosome 6 in the human major histocompatibility complex (MHC). HLA class Ib antigens resemble the HLA class Ia antigens in many ways, but several major differences have been described. This review will, in particular, discuss HLA-G and its role in human reproduction and in the human MHC. HLA-G seems to be important in the modulation of the maternal immune system during pregnancy and thereby the maternal acceptance of the semiallogenic fetus. Recent findings regarding aspects of HLA-G polymorphism, the possible significance of this polymorphism in respect to HLA-G function and certain complications of pregnancy (such as pre-eclampsia and recurrent spontaneous abortions (RSA)) are discussed together with possible importance to IVF. Finally, aspects of a possible role of HLA-G in organ transplantation and in inflammatory or autoimmune disease, and of HLA-G in an evolutionary context, are also briefly examined.

Female↗
PubMed2001

Genetic divergence and reproductive isolation between Anisakis brevispiculata and Anisakis physeteris (Nematoda: Anisakidae)s.

In order to assess the taxonomic status of Anisakis brevispiculata Dollfus, 1966 population samples of this taxon from central and south-eastern Atlantic ocean were compared at 22 enzymatic loci with samples belonging to Anisakis physeteris Baylis, 1923 from the Mediterranean sea and central-eastern Atlantic ocean. Very low interpopulational genetic divergence was observed both within A. brevispiculata (average D(Nei) = 0.008) and within A. physeteris (D(Nei) = 0.009) despite the geographic distance among the samples, indicating high levels of gene flow in both taxa. On the other hand, the average genetic distance between A. brevispiculata and A. physeteris was found to be D(Nei) = 0.80, a value generally observed between well differentiated congeneric species. The reproductive isolation between A. brevispiculata and A. physeteris is indicated by the following observations: (1) no F(1) hybrids or recombinant genotypes were until now observed; and (2) the two Anisakis species do not seem to share their definitive hosts. The main definitive host of A. brevispiculata is the pygmy sperm whale (Kogia breviceps), while for A. physeteris it is the sperm whale (Physeter catodon). Only adult males differ slightly in spicule length, while females and larval stages are not differentiated morphologically. Both A. brevispiculata and A.physeteris show a type II larva. The correct recognition of A. brevispiculata from A. physeteris and from other Anisakis species studied, in either sexes and at any life stage, is made easy by allozyme markers (e.g. Icdh, Gapdh, Sod-1, Np, Aat-2, Adk-2, fEst-2, PepB, PepC-2, Mpi). Diagnostic keys, which can be used for routine identification in the field of these Anisakis worms, based on genetic markers, are given.

Animals↗
PubMedDate not supplied

Current practices of commercial cryobanks in screening prospective donors for genetic disease and reproductive risk.

OBJECTIVE: To determine how the screening practices of commercial semen banks vary from published guidelines, which factors influence cryobanks to exclude prospective semen donors for genetic reasons, and the current role of clinical geneticists/genetic counselors in evaluating prospective semen donors. DESIGN: The genetic screening of prospective donors by commercial semen banks was evaluated using written questionnaires completed by bank directors. Responses were analyzed to determine exclusion criteria, adherence to published guidelines, and contribution of genetic professionals. SETTING AND PARTICIPANTS: Semen banks were selected on the basis of membership in the American Association of Tissue Banks and commercial use of semen for artificial insemination by donor. MAIN OUTCOME MEASURE: Semen bank practices as reported by commercial semen bank directors. RESULTS: Of 37 eligible banks, 16 responded. All screen prospective donors by medical/family history and physical examination, 94% have upper age limits; 63% examine for minor physical defects; 56% routinely karyotype; 81% screen men of ethnic groups at risk for Tay Sachs disease, sickle cell disease and thalassemia; 19% screen all donors; 25% screen all donors for cystic fibrosis and 50% only screen if family history positive. Donor rejection was based on three criteria: mode of inheritance of familial disorder, severity of disease, and availability of carrier/confirmatory testing of donor genotype. Ten of 16 banks have no genetic professional on staff. CONCLUSION: Commercial semen banks primarily rely on family history as the major exclusion criterion in genetic screening of donors. Considerable differences exist among semen bank practices in accordance with guidelines published by national agencies. Genetic professionals have a minimal effect overall on evaluation of semen donors.

Adult↗
PubMed2003

Genetic variability and reproductive mode of Aspergillus fumigatus.

Aspergillus fumigatus, an important human pathogen, has been the subject of numerous epidemiological studies. This review gives a summary of the techniques used for revealing the genetic variability of A. fumigatus, including multilocus enzyme electrophoresis and methods based on DNA hybridization and amplification. Such studies have provided raw data for examining the structure of A. fumigatus populations. Several methods have been described for distinguishing recombination from clonality in fungal populations. In our studies, both the index of association test and the parsimony tree length permutation test were used for examining the reproductive mode of Aspergillus fumigatus populations. The tests were performed on isoenzyme and sequence specific DNA primer analysis data gathered from the literature. Both tests, together with other observations, supported the premise that recombination played an important role in A. fumigatus populations. A so-called epidemic population structure was observed in local populations isolated from patients. The prevalence of a single or some related electrophoretic types in such environments was attributed to some kind of selection pressure. Network methods were also used successfully to visualize the recombining structures of A. fumigatus populations. The applied techniques did not enable us to distinguish between the alternative hypotheses of whether past meiotic exchanges, parasexuality or a cryptic sexual stage were responsible for the recombining population structure of A. fumigatus.

Aspergillus fumigatus↗
PubMed1979

Reproductive isolation with little genetic divergence in sympatric populations of brown trout (Salmo trutta).

Two reproductively isolated demes of brown trout coexist in a small Swedish mountain lake, Lake Bunnersjörna. We electrophoretically examined 102 specimens from that lake for 27 enzymes encoded by 54 loci. The two demes are fixed for different alleles at a lactate dehydrogenase locus (LDH-1); statistically significant allele frequency differences at five other loci further support the complete lack of gene flow between these demes. There are significant differences in growth rates between fish in the two demes, but no further morphological differentiation h-s been detected.--In light of these findings, the genetic distance between these populations is surprisingly small (Nei's I = 0.975). These demes represent one of the least genetically divergent, reproductively isolated sympatric pair of vertebrate populations that have been identified. The results are discussed from both an evolutionary and ecological perspective.

Alleles↗
PubMed2005

Reproductive cloning combined with genetic modification.

Although there is widespread opposition to reproductive cloning, some have argued that its use by infertile couples to have genetically related children would be ethically justifiable. Others have suggested that lesbian or gay couples might wish to use cloning to have genetically related children. Most of the main objections to human reproductive cloning are based on the child's lack of unique nuclear DNA. In the future, it may be possible safely to create children using cloning combined with genetic modifications, so that they have unique nuclear DNA. The genetic modifications could be aimed at giving such children genetic characteristics of both members of the couple concerned. Thus, cloning combined with genetic modification could be appealing to infertile, lesbian, or gay couples who seek genetically related children who have genetic characteristics of both members. In such scenarios, the various objections to human reproductive cloning that are based on the lack of genetic uniqueness would no longer be applicable. The author argues that it would be ethically justifiable for such couples to create children in this manner, assuming these techniques could be used safely.

Cloning, Organism↗
PubMed2007

Genetic structure and reproductive strategy of the ant Cardiocondyla elegans: strictly monogynous nests invaded by unrelated sexuals.

Cardiocondyla elegans is a Mediterranean ant that nests on river banks. It rears only wingless (ergatoid) males that live peacefully in the same nest as opposed to other species of the same genus, which have both peaceful, winged and mutually aggressive 'ergatoid' males. Using microsatellite analysis, we investigated the genetic structure of 21 colonies from three different locations as well as the parentage of sexuals of two colonies of C. elegans. We show that C. elegans is strictly monogynous, and that its nests can contain foreign sexuals. The presence of alien sexuals inside ant nests is described for the first time and probably counteracts inbreeding resulting from matings between siblings. In the laboratory, aggression tests showed that workers only allow alien males to enter their nests, while all winged female sexuals attempting to enter were attacked. Nevertheless, the presence of alien female sexuals in nests in the field seems to result from active carrying behaviour by workers during the reproductive period.

Animals↗
PubMed1991

Genetic effects for reproductive traits in beef cattle and predicted performance.

Reproductive data were collected on 4,595 cow exposures and subsequent calvings over four generations in a rotational crossbreeding study involving Angus, Brahman, Charolais and Hereford breeds. Direct and maternal additive (Ig and Mg) and nonadditive (Ih and Mh) genetic effects were estimated for calving rate, calf survival, weaning rate, calving assistance and calf birth date. Genetic effects were estimated by regressing individual animal response on the proportion of genes from breed of origin and gene combinations expected for the four breeds in offspring and in dams. Breed direct and maternal additive and nonadditive genetic effects were expressed as a deviation from the least squares mean. Brahman Ig effects decreased calving and weaning rate (-9.5 +/- 4.0 and -11.8 +/- 4.4%) but Mh effects for weaning rate that included Brahman were positive, ranging from 16.5 +/- 6.7% for Angus-Brahman to 27.8 +/- 6.9% for Brahman-Hereford. The Brahman Ig effect delayed calf birth date (9.8 +/- 2.1 d; P less than .01), whereas Angus and Hereford Ig effects influenced earlier calf birth dates (-4.3 +/- 1.9 and -4.1 +/- 1.9 d; P less than .05). Brahman combination Mh effects also influenced earlier calf birth dates (P less than .01). The Charolais Ig effect for calving assistance was positive (4.3 +/- 1.9%; P less than .05), whereas Angus-Brahman and Brahman-Charolais Mh effects for calving assistance were negative (-6.5 +/- 3.2 and -7.0 +/- 3.2%; P less than .05) and more desirable. Predicted reproductive traits for rotational mating systems were intermediate between predicted reproductive traits for two- and three-breed terminal crosses. Predicted calving and weaning rates were maximized when Brahaman first-cross and Charolais-Hereford cows were used in three-breed cross mating systems.

Animal Husbandry↗
PubMed1987

Simulation of genetic control of reproduction in beef cows. I. Simulation model.

A stochastic computer simulation model was constructed to predict the reproductive performance of beef cows as a function of the postpartum interval from calving to first estrus and the single-service conception rate. Phenotypic values for single-service conception rate were obtained by truncation of an assumed underlying normal phenotypic distribution at a point corresponding to a cumulative frequency of conception of .70. The underlying phenotypic distribution was derived as the sum of independent, normally-distributed additive genetic, permanent environmental and temporary environmental effects. The phenotypic frequency distribution for postpartum interval has been shown to be skewed toward large intervals. This distribution was simulated by combining normal distributions of additive genetic and permanent environmental effects with a strongly skewed Pearson III gamma distribution of temporary environmental effects. The simulated management system involved a 63-d breeding season, thereby allowing females up to three opportunities to conceive. The reproductive outputs that were simulated from postpartum interval and single-service conception rate included date of first service, first-service conception rate, number of services received, annual conception rate, calving date and postpartum interval. A normally-distributed 205-d weaning weight was also simulated and converted to an actual weaning weight by adjustment for calving date. General simulation results in terms of frequencies, means and standard deviations were compared with values found in the literature and found to provide a reasonable model of bovine reproductive performance.

Animals↗
PubMed1994

A genetic analysis of reproduction in Strongyloides ratti.

Strongyloides ratti has a complex life-cycle with two adult generations, one free-living and dioecious and one parasitic and female only. The parasitic females reproduce by parthenogenesis, but it is unclear whether this is mitotic or meiotic in nature. This question has been addressed genetically by analysing the progeny of parasitic females that were heterozygous at an actin locus for evidence of allelic segregation. Such progeny were similarly heterozygous showing that segregation had not occurred. It was therefore concluded that reproduction in the parasitic female of S. ratti is functionally mitotic.

Actins↗
PubMed1992

Integration of clinical genetics into assisted reproductive technologies: implications for nursing practice.

Assisted reproductive technologies (ART) have moved from the experimental periphery of clinical treatment to the center of routine practice in the field of reproductive endocrinology. With advances in technology, reduced operative risks, increasing third party reimbursement and increased accessibility to ART programs, a more heterogeneous group of couples is seeking these services. The traditional ART couple has been joined by a growing number of couples who are at risk for or affected by a genetic disorder. These individuals seek alternative methods of conception to minimize the risk of conceiving a child with a significant birth defect. Programs offering donor gamete, donor embryo, gestational carrier, and in the future, preimplantation genetic testing must be prepared for the unique needs of the "traditional" infertile and "nontraditional" fertile couple.

Chromosome Aberrations↗
PubMed1997

Postglacial genetic differentiation of reproductive ecotypes of kokanee Oncorhynchus nerka in Okanagan Lake, British Columbia.

Okanagan Lake, south-central interior of BC, contains two reproductive ecotypes of kokanee Oncorhynchus nerka; individuals spawn in tributary streams ('stream-spawners') as well as on shoreline gravel areas ('beach-spawners'). We tested the hypothesis that these sympatric ecotypes comprise a single panmictic population by assaying variation in morphological traits and at allozyme, mitochondrial and minisatellite DNA loci in fish collected from three stream-spawning and two beach-spawning sites. No morphological traits consistently distinguished the reproductive ecotypes with the exception of the number of anal fin rays which was greater in stream-spawning kokanee. Four of 18 allozyme loci screened were polymorphic, but no significant allele frequency differences were detected among populations within ecotypes or between ecotypes. Similarly, allele frequencies at two minisatellite DNA loci were not significantly different among populations or between ecotypes. By contrast, significant differences in the frequencies of mitochondrial DNA restriction fragment length polymorphism (mtDNA RFLP) haplo-types were detected between stream- and beach-spawners, but not among populations within ecotypes. Further, two RFLPs that distinguished stream- and beach-spawning adults were found in juvenile kokanee sampled from the limnetic zone of Okanagan Lake. The two mtDNA RFLPs and a d-loop sequence variant appear to be unique to Okanagan Lake Kokanee because we did not observe these haplotypes in sockeye salmon and kokanee sampled outside of Okanagan Lake. Our data suggest that: (i) there is restricted female-mediated gene flow between stream- and beach-spawning kokanee in Okanagan Lake, (ii) the forms have diverged within the lake basin since the retreat of the Wisconsinian glaciers (< approximately equal to 11 000 years ago), and (iii) distinct reproductive niches may promote divergence in north temperate freshwater fish faunas.

Animals↗
PubMed2004

Allochronic differentiation among Daphnia species, hybrids and backcrosses: the importance of sexual reproduction for population dynamics and genetic architecture.

Seasonal dynamics of the abundance, sexual reproduction and genetic architecture in a Daphnia hyalina-galeata hybrid complex were studied in the large and deep Lake Constance. We found evidence for the occurrence of first and second order hybridization. Our study revealed strong differences between the parental species not only regarding their seasonal dynamics, genetic architecture and diversity, but also their sexual reproductive behaviour. The overwintering D. hyalina showed low genetic diversity, no genetic differentiation during the season, and reproduced sexually in autumn, whereas D. galeata reached higher levels of genetic diversity, reproduced sexually in early summer, and exhibited changes in genetic structure during the season, but was only present from spring to autumn. However, in both species sexual reproduction was a rare event, and daphnids, including hybrids, reproduced predominantly asexually. This allows long-term persistence of hybrids as well without continuing hybridization events. Within all variables studied, F1 and F2 hybrids showed an intermediate pattern, whereas proposed backcross hybrids were more similar to their respective parentals. These differences in phenotype as well as significant differences in pairwise Fst values between parentals suggest that gene flow seems to be relatively low in the Lake Constance hybrid system. We found evidence for unidirectional introgression by backcrossing from D. galeata to D. hyalina and found a decrease in at least one of the proposed introgressed alleles in the hyalina-backcross while the season progressed. Our findings suggest allochronic differentiation within this hybrid population and different microevolutionary trajectories of the parental species, which will be discussed in the light of the ongoing reoligotrophication process of Lake Constance.

Animals↗