Genetic counselling for pulmonary arterial hypertension: a matter of variable variability

We report three cases which highlight the complex considerations surrounding genetic counselling for pulmonary arterial hypertension (PAH). The first counselee developed PAH symptoms shortly after his daughter’s death from PAH and was diagnosed with a delay of 1 year. An early diagnosis of familial PAH was established in the second counselee. Oral therapy was initiated immediately, and her functional status has since remained stable. The third counselee was a healthy woman who struggled to cope with her risk for familial PAH, having lost two siblings from the disease. These cases show that incomplete penetrance and variable expression need particular attention during clinical assessment and genetic counselling of heritable PAH patients and family members.     

Women’s work,child care,and helpers-at-the-nest in a hunter-gatherer society

Considerable research on helpers-at-the-nest demonstrates the positive effects of firstborn daughters on a mother’s reproductive success and the survival of her children compared with women who have firstborn sons. This research is largely restricted to agricultural settings. In the present study we ask: “Does ‘daughter first’ improve mothers’ reproductive success in a hunting and gathering context?” Through an analysis of 84 postreproductive women in this population we find that the sex of the first- or second-born child has no effect on a mother’s fertility or the survival of her offspring. We conclude that specific environmental and economic factors underlay the helpers-at-the-nest phenomenon.     

质疑、创新与合理性——纪念《植物学通报》创刊主编曹宗巽先生诞辰100周年

为纪念《植物学通报》创刊主编曹宗巽先生诞辰100周年, 该文回顾了作者与曹先生结识的机缘和承接其未竟的黄瓜(Cucumis sativus)单性花发育调控机制研究衣钵的过程, 以及从实验结果到传统解释的逻辑困境, 通过追溯曹先生当年带回国内的有关植物性别研究早期专著而找到问题源头的柳暗花明的经历。同时分享了由于这段独特而宝贵的研究经历而引发的对什么是科学研究这个基本问题的思考, 希望对有志于探索未知自然的年轻人有所裨益。     

Genetic architecture of local adaptation in lunar and diurnal emergence times of the marine midge Clunio marinus (Chironomidae, Diptera)

Circadian rhythms pre-adapt the physiology of most organisms to predictable daily changes in the environment. Some marine organisms also show endogenous circalunar rhythms. The genetic basis of the circalunar clock and its interaction with the circadian clock is unknown. Both clocks can be studied in the marine midge Clunio marinus (Chironomidae, Diptera), as different populations have different local adaptations in their lunar and diurnal rhythms of adult emergence, which can be analyzed by crossing experiments. We investigated the genetic basis of population variation in clock properties by constructing the first genetic linkage map for this species, and performing quantitative trait locus (QTL) analysis on variation in both lunar and diurnal timing. The genome has a genetic length of 167-193 centimorgans based on a linkage map using 344 markers, and a physical size of 95-140 megabases estimated by flow cytometry. Mapping the sex determining locus shows that females are the heterogametic sex, unlike most other Chironomidae. We identified two QTL each for lunar emergence time and diurnal emergence time. The distribution of QTL confirms a previously hypothesized genetic basis to a correlation of lunar and diurnal emergence times in natural populations. Mapping of clock genes and light receptors identified ciliary opsin 2 (cOps2) as a candidate to be involved in both lunar and diurnal timing; cryptochrome 1 (cry1) as a candidate gene for lunar timing; and two timeless (tim2, tim3) genes as candidate genes for diurnal timing. This QTL analysis of lunar rhythmicity, the first in any species, provides a unique entree into the molecular analysis of the lunar clock.     

Twin births to mothers who are twins: a registry based study.

OBJECTIVES: To estimate the risk of having twin infants for mothers who are twins; to investigate the genetic influence on twinning. DESIGN: Retrospective study of multiple births in two nationwide registries. SETTING: Sweden. SUBJECTS: Multiple births among 31,586 deliveries between 1973 and 1991 to women who were twins. MAIN OUTCOME MEASURES: Numbers of monozygotic and dizygotic twin births expected and estimated. RESULTS: Women who are dizygotic twins have a moderately increased risk of having twins (relative risk 1.30, 95% confidence interval 1.14 to 1.49) which seems to be completely the result of dizygotic twinning. When a mother is a monozygotic twin, her risk of having twins of the same sex is significantly increased (1.47; 1.10 to 1.97). This is the result of an excess of monozygotic twins (39 pairs estimated, 18 expected). CONCLUSIONS: Women who are twins have an increased risk of giving birth to twins. Genetic components of monozygotic and dizygotic twinning seem to be independent.     

The ends of a continuum: genetic and temperature-dependent sex determination in reptiles

Two prevailing paradigms explain the diversity of sex-determining modes in reptiles. Many researchers, particularly those who study reptiles, consider genetic and environmental sex-determining mechanisms to be fundamentally different, and that one can be demonstrated experimentally to the exclusion of the other. Other researchers, principally those who take a broader taxonomic perspective, argue that no clear boundaries exist between them. Indeed, we argue that genetic and environmental sex determination in reptiles should be seen as a continuum of states represented by species whose sex is determined primarily by genotype, species where genetic and environmental mechanisms coexist and interact in lesser or greater measure to bring about sex phenotypes, and species where sex is determined primarily by environment. To do otherwise limits the scope of investigations into the transition between the two and reduces opportunities to use studies of reptiles to advance understanding of vertebrate sex determination generally.     

Facial resemblance between women's partners and brothers

Research on optimal outbreeding describes the greater reproductive success experienced on average by couples who are neither too closely related, nor too genetically dissimilar. How is optimal outbreeding achieved? Faces that subtly resemble family members could present useful cues to a potential reproductive partner with an optimal level of genetic dissimilarity. Here, we present the first empirical data that heterosexual women select partners who resemble their brothers. Raters ranked the facial similarity between a woman's male partner, and that woman's brother compared to foils. In a multilevel ordinal logistic regression that modeled variability in both the stimuli and the raters, there was clear evidence for perceptual similarity in facial photographs of a woman's partner and her brother. That is, although siblings themselves are sexually aversive, sibling resemblance is not. The affective responses of disgust and attraction may be calibrated to distinguish close kin from individuals with some genetic dissimilarity during partner choice.     

Quantitative Genetics of Sex Ratio Traits in the Parasitic Wasp, Nasonia Vitripennis

We detected significant parent-offspring regressions for the first sex ratio (the sex ratio produced by a female in a fresh host) and the second sex ratio (the sex ratio produced by a female in a previously parasitized host) in the parasitic wasp, Nasonia vitripennis. For both traits, estimates of the narrow-sense heritability range from &0.05 to &0.15 (depending on how the data are analyzed). The study population was derived from isofemale strains created from wasps captured in a single bird nest. The same population exhibited no significant parent-offspring regression for the brood sizes associated with the first and second sex ratios. There may be a significant negative parent-offspring regression for diapause proportion in the first sex ratio broods. The estimates of the genetic correlations between first and second sex ratios are positive although almost all are not significantly different from 0.0. To our knowledge, this study is the first ``fine-scale' analysis of genetic variation for sex ratio traits in any species of insect. Such studies are an essential part of the assessment of the validity of claims that sex ratio traits are locally optimal.     

Parents’ genetic dissimilarity and offspring sex in a polygynous mammal

Offspring quality may benefit from genetic dissimilarity between parents. However, genetic dissimilarity may trade‐off with additive genetic benefits. We hypothesized that when sexual selection produces sex‐specific selective scenarios, the relative benefits of additive genetic vs. dissimilarity may differ for sons and daughters. Here we study a sample of 666 red deer (Cervus elaphus) microsatellite genotypes, including males, females and their foetuses, from 20 wild populations in Spain (the main analyses are based on 241 different foetuses and 190 mother‐foetus pairs). We found that parental lineages were more dissimilar in daughters than in sons. On average, every mother was less related to her mate than to the sample of fathers in the population when producing daughters not sons. Male foetuses conceived early in the rutting season were much more inbred than any other foetuses. These differences maintained through gestation length, ruling out intrauterine mortality as a cause for the results, and indicating that the potential mechanism producing the association between parents’ dissimilarity and offspring sex should operate close to mating or conception time. Our findings highlight the relevance of considering the sex of offspring when studying genetic similarity between parents.     

Genetic mapping of sex determination in a wild strawberry, Fragaria virginiana, reveals earliest form of sex chromosome

The evolution of separate sexes (dioecy) from hermaphroditism is one of the major evolutionary transitions in plants, and this transition can be accompanied by the development of sex chromosomes. Studies in species with intermediate sexual systems are providing unprecedented insight into the initial stages of sex chromosome evolution. Here, we describe the genetic mechanism of sex determination in the octoploid, subdioecious wild strawberry, Fragaria virginiana Mill., based on a whole-genome simple sequence repeat (SSR)-based genetic map and on mapping sex determination as two qualitative traits, male and female function. The resultant total map length is 2373 cM and includes 212 markers on 42 linkage groups (mean marker spacing: 14 cM). We estimated that approximately 70 and 90% of the total F. virginiana genetic map resides within 10 and 20 cM of a marker on this map, respectively. Both sex expression traits mapped to the same linkage group, separated by approximately 6 cM, along with two SSR markers. Together, our phenotypic and genetic mapping results support a model of gender determination in subdioecious F. virginiana with at least two linked loci (or gene regions) with major effects. Reconstruction of parental genotypes at these loci reveals that both female and hermaphrodite heterogamety exist in this species. Evidence of recombination between the sex-determining loci, an important hallmark of incipient sex chromosomes, suggest that F. virginiana is an example of the youngest sex chromosome in plants and thus a novel model system for the study of sex chromosome evolution.     

The question of virginity testing in Turkey

Pre-marital sex for a woman is regarded as wrong in my country. As a result, it is socially forbidden for a woman to engage in this act. In order to present a woman as a virgin on her marriage day, she is subjected to pressure, and put under control both by her family and societal norms. However, a man is free and never made to suffer any of the above. A woman found to be a virgin on her first night of marriage is seen as a normal person while one suspected to have lost her virginity is made to undergo a series of medical examinations to bring clarity to her situation.     

Constrained sex allocation in a parasitoid due to variation in male quality

The theory of constrained sex allocation posits that when a fraction of females in a haplodiploid population go unmated and thus produce only male offspring, mated females will evolve to lay a female-biased sex ratio. I examined evidence for constrained sex ratio evolution in the parasitic hymenopteran Uscana semifumipennis. Mated females in the laboratory produced more female-biased sex ratios than the sex ratio of adults hatching from field-collected eggs, consistent with constrained sex allocation theory. However, the male with whom a female mated affected her offspring sex ratio, even when sperm was successfully transferred, suggesting that constrained sex ratios can occur even in populations where all females succeed in mating. A positive relationship between sex ratio and fecundity indicates that females may become sperm-limited. Variation among males occurred even at low fecundity, however, suggesting that other factors may also be involved. Further, a quantitative genetic experiment found significant additive genetic variance in the population for the sex ratio of offspring produced by females. This has only rarely been demonstrated in a natural population of parasitoids, but is a necessary condition for sex ratio evolution. Finally, matings with larger males produced more female-biased offspring sex-ratios, suggesting positive selection on male size. Because the great majority of parasitic hymenoptera are monandrous, the finding of natural variation among males in their capacity to fertilize offspring, even after mating successfully, suggests that females may often be constrained in the sex allocation by inadequate number or quality of sperm transferred.     

Evolutionarily stable mixed mating in a variety of genetic systems

Many species display a mixture of close inbreeding and outbreeding which is referred to as mixed mating. For selfing species, models predict that such mixed mating systems can be stable. Conversely, models considering separate sex species have not been able to explain mixed mating systems. This failure may be a result of the unrealistic assumption that recurrent inbreeding does not increase the inbreeding coefficient. Here we show that mixed mating is expected in separate sex systems when recurrent inbreeding is taken into account. A female that allows her brother to sibmate with her gives an extra mating opportunity to said brother. This kin selective advantage should be strongest in genetic systems where the male is more related to the female. In support of this idea, we find that inbreeding evolves most easily in selfers, followed by diploid sibmating, followed by haplodiploid sibmating. Consideration of published values for the regression of fitness on inbreeding coefficient suggests that many species fall in a range where some selfing/sibmating is optimal.     

Evolution of the sterile caste

Biased sex ratios are expected to affect the conditions of the evolution of worker behaviour in malehaploid populations. In a subsocial, malehaploid species an association to female-biased brood sex ratios favours the evolution of worker behaviour. There are various reasons to expect such an association. The critical worker efficiency threshold required for worker behaviour to evolve is lower when looked at from the viewpoint of the mother than from that of the daughter. In this mother-daughter conflict, the mother can expect some help from her other offspring to resolve the conflict in her favour. In semisocial species the sex ratio biases have a less significant role and the worker behaviour can evolve more easily in malehaploid than in diploid populations. Furthermore, limited dispersal (due to the risks attached to it) is expected to favour worker behaviour in malehaploid but inbreeding in diploid populations. In addition to the genetic mechanisms that determine the critical worker efficiency threshold, it is essential to pay attention to those ecological factors that affect the actual worker efficiency in nature. Several such factors exist but it is not easy to associate them with the common occurrence of eusocial species in the Hymenoptera.     

Detection of a common mutation of the catalase gene in Japanese acatalasemic patients

Summary Acatalasemia was one of the earliest described genetic enzyme defects. In 1990, a causal point mutation (a splicing mutation) was first reported in a Japanese patient with acatalasemia. In the present study, the polymerase chain reaction and single-strand conformation polymorphism analysis were used to determine whether the same point mutation was present in unrelated Japanese patients. The subjects studied were the previously examined acatalasemic female, her brother, who is hypocatalasemic, and two other unrelated acatalasemic patients. A single G to A point mutation at the fifth position of intron 4, identical to that previously found, was present in all the studied patients. This finding strongly suggests that only a single mutated allele has spread in the Japanese population.     

A current perspective on genetic testing for breast and ovarian cancer: the oral contraceptive decision

A clinician faces a problem in how best to counsel the woman with a family history of breast or ovarian cancer about her options for pregnancy prevention. The physician must guide her as she makes new and complex decisions. Recent data strongly support an amplified effect of the estrogens in oral contraceptives for the woman with a genetic risk for breast cancer. Nonetheless, a woman's immediate need to prevent pregnancy may be much more important to her than worrying about the long-term risk of breast cancer. Another factor is that oral contraceptives prevent ovarian cancer, so the physician may wish to prescribe them to protect her from ovarian cancer. In some genetic backgrounds, however, oral contraceptives not only do not prevent ovarian cancer, but they may raise the risk of breast cancer so significantly that they should not be taken. With other genetic backgrounds, oral contraceptives will protect the woman from ovarian cancer without much effect on her breast cancer risk. When does each of these cancer risks or benefits become significant? The clinician can provide an important benefit to a woman who must prevent pregnancy yet worries about her cancer risk. The physician can help her evaluate the evidence, with its gaps and uncertainties, in the context of her own preferences. To assist in this evaluation, this decision aid provides base-line estimates of the cancer risk that accompanies each of a woman's options. In some cases, genetic testing is likely to provide valuable information as she makes choices about contraception and the risks vs. benefits of different alternatives available to her.     

Patterns of sex ratio variation and genetic diversity in the dioecious forest perennial <Emphasis Type="Italic">Mercurialis perennis</Emphasis>

In small populations of plant species with separate sexes, it can be expected that besides the local environment also stochastic events influence population sex ratios. Biased sex ratios may in turn negatively affect genetic diversity due to increased genetic drift and, in clonal plants, due to reduced sexual reproductive output. Empirical evidence for these processes is scarce, however. We investigated the pattern of sex ratio variation and the distribution of genetic variation of the dioecious clonal forest herb Mercurialis perennis using AFLP markers. Analysis of molecular variance indicated a pronounced genetic structure. Overall within-population genetic diversity was moderate and local sex ratios were slightly male biased. The proportion of male to female plants in large populations slightly increased with increasing light penetration to the herb layer. Small populations, on the contrary, displayed high variability in sex ratios, unrelated to the local light environment. Genotypic diversity decreased with more male-biased sex ratios. We conclude that stochastic events related to small population size and the local forest environment, related to canopy closure, affect the proportion of female plants and indirectly influence local genotypic diversity, likely through the degree of sexual reproduction. This is one of the first studies to report a clear association between gender proportions and genetic diversity of a dioecious plant species in a fairly large survey.     

The quantitative analysis of polymorphism on human chromosomes 1, 9, 16, and Y

Summary A paracentric inversion of chromosome 5 was detected after RHG banding in a subject affected by Klinefelter's syndrome. The inversion was also observed in the patient's mother, and was confirmed by QFQ-and RBA-banding techniques.A second paracentric inversion affecting chromosome 7 was detected in a woman with Turner's syndrome. The same structural anomaly was found in her father and her half-brother.The possible relationship between sex chromosome nondisjunction and paracentric inversion is discussed.Furthermore, the inversion of chromosome 7 reproduces exactly the chromosome 7 of the gorilla, which is presumed to be ancestral to the human 7. This therefore appears to be the first reported case of reverse chromosomal mutation.     

Sperm status regulates sexual attraction in Caenorhabditis elegans

Mating behavior of animals is regulated by the sensory stimuli provided by the other sex. Sexually receptive females emit mating signals that can be inhibited by male ejaculate. The genetic mechanisms controlling the release of mating signals and encoding behavioral responses remain enigmatic. Here we present evidence of a Caenorhabditis elegans hermaphrodite-derived cue that stimulates male mating-response behavior and is dynamically regulated by her reproductive status. Wild-type males preferentially mated with older hermaphrodites. Increased sex appeal of older hermaphrodites was potent enough to stimulate robust response from mating-deficient pkd-2 and lov-1 polycystin mutant males. This enhanced response of pkd-2 males toward older hermaphrodites was independent of short-chain ascaroside pheromones, but was contingent on the absence of active sperm in the hermaphrodites. The improved pkd-2 male response toward spermless hermaphrodites was blocked by prior insemination or by genetic ablation of the ceh-18-dependent sperm-sensing pathway of the hermaphrodite somatic gonad. Our work suggests an interaction between sperm and the soma that has a negative but reversible effect on a hermaphrodite-derived mating cue that regulates male mating response, a phenomenon to date attributed to gonochoristic species only.     

Infanticide in chimpanzees: Review of cases and a new within-group observation from the Kanyawara study group in Kibale National Park

A prolonged attack on a mother and 2-year-old infant that resulted in the death of the infant was observed in the Kanyawara study group in Kibale National Park. The mother was a border-area resident who was first observed associating with unit-group males six years previously. The attackers were an adult male and an adult female with a 6-week-old infant clinging ventrally to her. The attack was unusual in several respects: it is the first time a male and a female chimpanzee have been observed cooperating closely in an infanticidal attack; the adult female initially attempted to intervene in the victim's behalf, but later joined in the attack after receiving aggression from the male; and the episode was longer in duration than other reported cases. In the year following the incident, the mother did not increase her association with community males, but was seen with the male who killed her infant. The relevance of these observations to sexual selection-based explanations for infanticide in chimpanzees is discussed.