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PubMed1998

Ecological and genetic evidence for clonal reproduction in Gyrodactylus gasterostei Glaser, 1974.

Reproduction of isolated Gyrodactylus gasterostei from the three-spined stickleback, Gasterosteus aculeatus, has been investigated. Three lineages of isolated parasites, without opportunity for cross- or self-fertilisation, continued to reproduce for up to 19 generations (224 births) until experiments were discontinued. Most parasites gave birth to two daughters only, although four individuals in one lineage gave birth three times. After the final birth the empty uterus expanded, while a large oocyte remained in the seminal receptacle and appeared capable of development. Reproduction by isolated flukes was further analysed using quantitative genetic techniques, applied to the hamuli and marginal hooks. The variance of hamulus and marginal hook dimensions in lineages of isolated flukes (which, if sexual must be highly inbred) was similar to that observed in natural populations. Crude heritability appeared high, but a significant relationship between hook size and environmental temperature was noted, and when this was controlled for, the heritability of all characters became negligible. Genetic drift was not observed over 17 generations and variance within isolated lines accounted for almost all of the total variance. Genes controlling hamulus or marginal hook dimensions did not progress to fixation, although the number of generations (more than 10) was sufficient to ensure homozygosity if self-fertilisation were occurring. These observations indicate that reproduction by isolated G. gasterostei continues indefinitely, but does not involve sex. The limited variance of natural populations suggests that these are also clonal with observed variation being largely environmental. Sexual reproduction may therefore be rare in G. gasterostei.

Animals↗
PubMed1983

Genetic effects of radiocarbon in reproductive cells of male mice.

The genetic effect of incorporated radiocarbon was studied after single, long-term (33 days) and chronic (6 and 12 months) treatment of male mice (CBA X C57B1) F1 with [14C]glucose. The genetic effect in male germ cells was estimated by 3 tests: DLM frequency in post- and pre-meiotic cells, RT frequency in stem spermatogonia and frequency of abnormal sperm heads. Absorbed doses in the gonads were: 0.22, 0.50 and 1.01 Gy, after a single exposure; 0.74 and 1.47 Gy, after long-term exposures; and 0.006 and 0.031 Gy, after chronic exposure for 6 months; and 0.013 and 0.066 Gy, for 12 months. The results suggest that DLM frequency in post-meiotic cells increased linearly with increasing the dose of 14C single and long-term exposures at a dose of 1.47 Gy only. A chronic treatment with [14C]glucose induced no increase in DLM frequency. RT frequency in stem spermatogonia was statistically significantly higher than the control level after the single and long-term exposure to 14C. A comparison of the results with the results of external single and chronic gamma-irradiation allows the conclusion that the relative genetic efficiency of radiocarbon as compared with that of gamma-rays is about 1.

Animals↗
PubMed2005

Mobile genetic elements and sexual reproduction.

Transposable elements (TE) are prominent components of most eukaryotic genomes. In addition to their possible participation in the origin of sexual reproduction in eukaryotes, they may be also involved in its maintenance as important contributors to the deleterious mutation load. Comparative analyses of transposon content in the genomes of sexually reproducing and anciently asexual species may help to understand the contribution of different TE classes to the deleterious load. The apparent absence of deleterious retrotransposons from the genomes of ancient asexuals is in agreement with the hypothesis that they may play a special role in the maintenance of sexual reproduction and in early extinction for which most species are destined upon the abandonment of sex.

Animals↗
PubMed1994

Female reproductive profile in a fertile, genetically obese line of rats.

The female reproductive profile of a fertile genetically obese line of rats, named beta, is characterized. Hypophysis, ovaries, oviducts, and uteri weights do not differ from those of nonobese controls. Histological features in ovary, uterus, and vagina in beta line and alpha controls are similar, in agreement with classical descriptions in the subject. Vaginal opening, number of estrus, number of corpora lutea at ovulation time, and pregnancy patterns (i.e., ovary weight, number of corpora lutea, sites of implantation, and living fetuses, as well as productivity, fertility, litter size, and preweaning mortality) show no significant differences between obese and nonobese animals. From a reproductive standpoint, obese beta line would behave as nonobese. Up to now beta would represent the only fertile genetically obese line of rats, appearing as a profitable biological model to widen and deepen reproductive analysis on obesity.

Animals↗
PubMed2002

Relationship between serum hormone concentrations, reproductive history, alcohol consumption and genetic polymorphisms in pre-menopausal women.

Reproductive characteristics, alcohol intake and polymorphisms in genes encoding sex-steroid metabolizing enzymes might influence the risk of hormone-related cancers by changing circulating concentrations of sex hormones. The relationship between these factors and serum concentrations of estradiol, progesterone, androstenedione, testosterone and DHEA was evaluated in a cross-sectional study of 218 pre-menopausal women from Kaiser Permanente Health Plan in Portland, Oregon. Risk factor information was obtained from questionnaires and hormone serum concentrations were determined by radioimmunoassays. Genotypes for CYP11A 5'UTR(tttta)n, CYP17 5'-UTR -34 T>C, CYP19 IVS4(ttta)n, CYP1B1 (L432V and S453N) and COMT (V158M) were determined from genomic DNA samples. Increasing number of full-term pregnancies was associated with a significant decrease in late-follicular progesterone levels (p-trend = 0.03). Increasing alcohol consumption was associated with higher estradiol levels averaged through the menstrual cycle (p-trend = 0.009) and higher progesterone levels during luteal phase (p-trend = 0.04). Androstenedione and testosterone levels were higher among light to moderate drinkers compared to non-drinkers, although we only observe a significant trend with increasing levels of alcohol consumption for androstenedione. Women heterozygous or homozygous for the CYP1B1 L432V or the S453N polymorphisms had increased luteal estradiol levels (p-value = 0.04 for L432V and 0.04 for S453N). None of the other factors evaluated was significantly associated with serum concentration of hormones. In conclusion, results from this cross-sectional study of pre-menopausal women provide support for an association between light to moderate alcohol intake and elevated levels of estrogen and androgen levels. Our data suggest that circulating levels of progesterone might be related to parity and alcohol consumption, however the biological plausibility of the observed associations is unclear. We found little support for an influence of the evaluated genetic polymorphisms in the steroid synthesis and metabolism pathway on serum hormone levels, except for a possible effect of the CYP1B1 L432V and S453N polymorphisms on serum estradiol levels.

Adolescent↗
PubMed2006

Quantitative genetics of age at reproduction in wild swans: support for antagonistic pleiotropy models of senescence.

Why do individuals stop reproducing after a certain age, and how is this age determined? The antagonistic pleiotropy theory for the evolution of senescence predicts that increased early-life performance should be accompanied by earlier (or faster) senescence. Hence, an individual that has started to breed early should also lose its reproductive capacities early. We investigate here the relationship between age at first reproduction (AFR) and age at last reproduction (ALR) in a free-ranging mute swan (Cygnus olor) population monitored for 36 years. Using multivariate analyses on the longitudinal data, we show that both traits are strongly selected in opposite directions. Analysis of the phenotypic covariance between these characters shows that individuals vary in their inherent quality, such that some individuals have earlier AFR and later ALR than expected. Quantitative genetic pedigree analyses show that both traits possess additive genetic variance but also that AFR and ALR are positively genetically correlated. Hence, although both traits display heritable variation and are under opposing directional selection, their evolution is constrained by a strong evolutionary tradeoff. These results are consistent with the theory that increased early-life performance comes with faster senescence because of genetic tradeoffs.

Aging↗
PubMed2004

Reproductive autonomy rights and genetic disenhancement: sidestepping the argument from backhanded benefit.

John Robertson has famously argued that the right to reproductive autonomy is exceedingly broad in scope. That is, as long as a particular reproductive preference such as having a deaf child is "determinative" of the decision to reproduce then such preferences fall under the protective rubric of reproductive autonomy rights. Importantly, the deafness in question does not constitute a harm to the child thereby wrought since unless the child could be born deaf he or she would otherwise never have existed--his or her prospective parents would simply have chosen to abort. As such, for this child, being born deaf counts as a benefit, albeit of the "backhanded" variety, since the only other practical alternative is nonexistence. In what follows, I want to investigate this argument in detail. The target of my investigation will be the possible future use of gene therapy technology to "disenhance" one's offspring. I intend to show that the apparently unlimited right to reproductive autonomy, that is, the right to choose both the quantity and qualities of future offspring, entailed by the argument from backhanded benefit can in fact be "sidestepped" through considering what sorts of reproductive practices we as a society ought to allow.

Child↗
PubMed2000

Of maize and men: reproductive control and the threat to genetic diversity.

The genetic diversity argument (GDA) is one of the most commonly voiced objections to advances in reproductive and genetic technologies. According to the argument, scientific and technological developments in the realm of genetics and human reproduction will lead to lower genetic diversity, which will threaten the health and survivability of the human population. This discussion explicates and analyzes the GDA and challenges its empirical assumptions. It also discusses the possible significance of the GDA in our overall thinking about genetics and human reproduction and examines two proposals for preserving "useful" genes.

Eugenics↗
PubMed2005

Sexual reproduction, clonal diversity and genetic differentiation in patchily distributed populations of the temperate forest herb Paris quadrifolia (Trilliaceae).

Clonal plant species have been shown to adopt different strategies to persist in heterogeneous environments by changing relative investments in sexual reproduction and clonal propagation. As a result, clonal diversity and genetic variation may be different along environmental gradients. We examined the regional and local population structure of the clonal rhizomatous forest herb Paris quadrifolia in a complex of forest fragments in Voeren (Belgium). Relationships between population size (the number of shoots), shoot density (the number of shoots per m2) and local growth conditions were investigated for 47 populations. Clonal diversity and genetic variation within and among 19 populations were investigated using amplified fragment length polymorphism markers. To assess the importance of sexual reproduction, seed set, seed weight and germination success were determined in 18 populations. As predicted, local growth conditions largely affected population distribution, size and density of P. quadrifolia. Populations occurring in moist and relatively productive sites contained significantly more shoots. Here, shoots were also much more sparsely distributed compared to populations occurring in dry and relatively unproductive sites, where shoots showed a strongly aggregated distribution pattern. Clonal diversity was relatively high, compared with other clonal species (G/N ratio=0.43 and Simpson's D=0.81). Clonal diversity significantly (P<0.01) decreased with increasing shoot density while molecular genetic variation was significantly (P<0.01) affected by population size and local environmental conditions. Lack of recruitment and out-competition of less-adapted genotypes may explain the decreased genetic variation in dry sites. Analysis of molecular variance revealed significant genetic variation among populations (PhiST=0.42, P<0.001), whereas pairwise genetic distances were not correlated to geographic distances, suggesting that gene flow among populations is limited. Finally, the number of generative shoots, the number of seeds per fruit and seed weight were significantly and positively related to population size and local growth conditions. We conclude that under stressful conditions populations of clonal forest plant species can slowly evolve into remnant populations characterized by low levels of genetic variation and limited sexual reproduction. Conservation of suitable habitat conditions is therefore a prerequisite for effective long-term conservation of clonal forest plant species.

Magnoliopsida↗
PubMed1999

Reproductive biology and conservation genetics of Goodyera procera (Orchidaceae).

Goodyera procera is an endangered terrestrial orchid in Hong Kong. Information on its reproductive biology and pattern of genetic variation is needed to develop efficient conservation strategies. Pollination experiments showed that the species is self-compatible, but dependent on pollinators for fruit set. Bagged plants produced no fruits. Artificial pollinations resulted in 92% fruit set through selfing, 94% with geitonogamous pollination, and 95% following xenogamous pollination. Fruit set in the open-pollinated control was 75% at the same sites. Allozyme electrophoresis and random amplified polymorphic DNA (RAPD) were used to evaluate genetic variation and structure of 15 populations of Goodyera procera. Despite its outbreeding system, allozyme data revealed low variation both at the population (P = 21.78%, A = 1.22, and H = 0.073) and species (P = 33%, A = 1.33, and H = 0.15) levels, in comparison with other animal-pollinated outbreeding plant species. However, RAPD variation was relatively high (P = 55.13% and H = 0.18 at the population level, and P = 97.03% and H = 0.29 at the species level). G(ST) estimates indicated high levels of genetic differentiation among populations (G(ST) = 0.52 and I = 0.909 ± 0.049 based on allozyme data, and G(ST) = 0.39 and I = 0.859 ± 0.038 based on RAPD data), much above the average for outcrossing species, suggesting that gene flow was limited in this species. Based on these data, suitable strategies were developed for the genetic conservation and management of the species.

Journal Article↗
PubMed2006

Genetic diversity and the reproductive system in related species of antirrhinum.

BACKGROUND AND AIMS: Seven related species of Antirrhinum (A. siculum, A. majus, A. latifolium, A. linkianum, A. litigiosum, A. cirrhigherum and A. tortuosum) were studied in order to compare levels of genetic variation and its partitioning in them, and to check relationships between genetic patterns and the reproductive system. METHODS: Eight hundred and fifty-one plants were screened for variability at 13 allozyme loci by means of horizontal starch gel electrophoresis. Parameters of genetic diversity and its partitioning, the inbreeding coefficient as well as an indirect estimate of gene flow based on the equation: Nm = (1 - G(ST))/4G(ST), were calculated. KEY RESULTS: Genetic variability in A. siculum was found to be the lowest known in the genus. Mean values of F(IT) and F(IS) were mostly positive and not significantly different from zero. Population differentiation (F(ST)) ranged between 6.1 in A. tortuosum and 17.6 in A. linkianum. The inbreeding coefficient within populations ranged between F(IS) = -0.5 in A. tortuosum and F(IS) = 1 in A. siculum. Estimates of gene flow ranged between Nm = 15 in A. majus (considered as very high) to Nm = 0.42 in A. siculum (considered as low). CONCLUSIONS: Correlation was found between levels of diversity and differentiation on one hand, and the reproductive system of the studied taxa on the other. Striking differences among species in the inbreeding coefficient (F(IS)) show different reproductive systems, which mostly support previous reports. Strategies for the conservation of A. siculum are recommended, such as preservation of natural populations as well as ex situ preservation of seeds from different populations.

Antirrhinum↗
PubMed2003

Genetic factors in assisted reproduction.

It is still unclear whether the procedures of assisted reproduction increase the risk of congenital malformations. Thus, it remains to be clarified whether an increased risk, if any, of congenital malformations in these children is caused by the procedure of assisted reproduction itself or by the underlying maternal and paternal background. From the genetic point of view, infertility patients seeking assisted reproduction have to be classified as a high-risk group. The prevalence of numerical chromosomal abnormalities is around 10% in these patients, compared with 0.85% in the general population. The prevalence of structural chromosomal abnormalities is around 0.1% in the general population and is increased up to 1% in patients seeking assisted reproduction. In addition, patients with microdeletions of the Y-chromosome or mutations in the cystic fibrosis transmembrane-conductance regulator gene are likely to be encountered at the fertility clinic. Therefore, genetic screening and counselling should be routinely offered to infertility patients. They also need to understand that parental factors can be transferred to offspring that would most likely not have been conceived by natural means.

Adult↗
PubMed2005

A DNA-launched reverse genetics system for porcine reproductive and respiratory syndrome virus reveals that homodimerization of the nucleocapsid protein is essential for virus infectivity.

Reverse genetic systems were developed for a highly virulent 'atypical' porcine reproductive and respiratory syndrome virus (PRRSV). The full-length genome of 15395 nucleotides was assembled as a single cDNA clone and placed under either the prokaryotic T7 or eukaryotic CMV promoter. Transfection of cells with the RNA transcripts or the DNA clone induced cytopathic effects and produced infectious progeny. The reconstituted virus was stable and grew to the titer of the parental virus in cells. Upon infection, pigs produced clinical signs and lung pathology typical for PRRSV and induced viremia and specific antibodies. Previously, we showed that the PRRSV nucleocapsid (N) protein forms homodimers via both noncovalent and covalent interactions and that cysteine at position 23 is responsible for the covalent interaction. The functional significance of cysteines of N for PRRSV infectivity was assessed using the infectious cDNA clone. Each cysteine of N at positions 23, 75, and 90 was replaced with serine and the individual mutation was incorporated into the cDNA clone such that three independent cysteine mutants were constructed. When transfected, the wild type and C75S clones induced cytopathic effects and produced infectious virus with indistinguishable plaque morphology. In contrast, the C23S mutation completely abolished infectivity of the clone, indicating that C23-mediated N protein homodimerization plays a critical role in PRRSV infectivity. Unexpectedly, the C90S mutation also appeared to be lethal for virus infectivity. Genome replication and mRNA transcription were both positive for the replication-defective C23S and C90S mutants. The data suggest that, in addition to homodimerization, the PRRSV N protein may also undergo heterodimerization with another structural protein using cysteine 90 and that the N protein heterodimerization is essential for PRRSV infectivity.

Animals↗
PubMed1999

The ethics of therapeutic and reproductive human cloning.

Neither therapeutic cloning nor reproductive cloning necessarily pose insurmountable ethical obstacles. Two defences of therapeutic cloning are considered. The first defence, the argument from property, is rejected because it entails morally counter-intuitive consequences. We should prefer a 'balance of reasons' defence which leaves room for the view that human life has intrinsic value. Reproductive cloning is best defended by an appeal to the right to procreative autonomy. The sorts of harms it is feared clones will suffer are also suffered by children conceived through natural means, even when these harms were preventable. The right to reproductive autonomy disallows state control of any form of reproduction for the reasons of child welfare discussed.

Cloning, Organism↗