The effect of reproductive compensation on recessive disorders within consanguineous human populations

We investigate the effects of consanguinity and population substructure on genetic health using the UK Asian population as an example. We review and expand upon previous treatments dealing with the deleterious effects of consanguinity on recessive disorders and consider how other factors, such as population substructure, may be of equal importance. For illustration, we quantify the relative risks of recessive lethal disorders by presenting some simple calculations that demonstrate the effect 'reproductive compensation' has on the maintenance of recessive alleles. The results show how reproductive compensation can effectively counteract the purging of deleterious alleles within consanguineous populations. Whereas inbreeding does not elevate the equilibrium frequency of affected individuals, reproductive compensation does. We suggest this effect must be built into interpretations of the incidence of genetic disease within populations such as the UK Asians. Information of this nature will benefit health care workers who inform such communities.     

Interpreting reproductive allometry: Individual strategies of allocation explain size-dependent reproduction in plant populations

Size-dependent or allometric relationships between reproductive and vegetative size are extremely common in plant populations. Reproductive allometry where plant size differences are due to environmental variability has been interpreted both as an adaptive strategy of plant growth and allocation, and as the product of fixed developmental constraints. Patterns of development are crucial in defining reproductive allometry but development is not fixed across individuals. For example, environmental adversity (e.g. resource impoverishment) tends to favor reproduction at relatively small sizes – an adaptive response to environmental adversity. While small individuals may have lower reproductive output than large individuals, all plants should maximize their reproductive output and relative allocation to reproduction may be constant across sizes. Thus, where individual plants within a population initiate reproduction at different sizes, no significant reproductive allometry is an appropriate null expectation. Reproductive allometry occurs in plant populations where initiating reproduction at small sizes yields relatively high or low reproductive size at final development. Both of these outcomes are common in plant populations. Our interpretation of reproductive allometry combines previous adaptive and developmental constraint interpretations, and is the first to successfully explain the range of relationships in plant populations where relative allocation has been observed to increase, decrease or remain constant will increasing plant size.     

Early reproduction and increased reproductive allocation in metal-adapted populations of the terrestrial isopod Porcellio scaber

Organisms inhabiting metal-contaminated areas can be stressed by metal exposure and are possibly subject to selection, resulting in increased metal tolerance and changes in growth and/or reproduction characteristics. In a previous study it was found that in the terrestrial isopod Porcellio scaber, sampled from the vicinity of a zine smelter, the body size was small and the brood size was large compared to isopods from a reference area. To assess whether these differences were due to genetic differentiation between strains, isopods collected from a reference wood, a zinc smelter area and a lead mine were cultured on non-polluted food, while growth, reproduction and metal concentrations were studied in first and second laboratory generations. The isopods from the three populations differed in age and weight at first reproduction, although there were hardly any differences in growth. The females of the mine and the smelter population started to reproduce earlier, at a lower weight, which resulted in fewer young per female. However, reproductive allocation (=wight of young relative to the weight of the mother) was higher in mine and smelter isopods. We conclude that the isopods at the metal-contaminated sites have been selected for early reproduction and increased reproductive allocation. The results indicate that populations inhabiting metal-polluted sites have probably undergone evolutionary changes. This study showed that growth and reproduction characteristics of different populations under laboratory conditions may provide information on selection processes in the field.     

Processes of the differentiation and reproduction of different types of muscle cells

The present review is regarding a vast evidence on reproduction, differentiation, and regenerative capacity of various muscle cells on the basis of A. A. Zavarzin's (Senior) parallelism conception. It is specially emphasized that parallelism in the subcellular organization of contractile structures of somatic and of heart muscle goes well together with a totally different principle of organization of these cellular elements (symplasts, or cells, respectively), and with different mechanisms of their histogenesis and regeneration (proliferation of, respectively, myoblasts, or immature myocytes). According to their ultrastructure and pattern of interrelation between proliferation and differentiation process, muscles of lymphatic hearts are closer to somatic muscles rather than to ordinary myocardium. Special attention is called to paradoxical situations, such as the presence of satellite-like cells in the myocardium of Decapoda, DNA-synthesizing capacity observed in the nuclei of growing somatic muscles of the silkworm, or DNA-synthesizing and chromosome-reproducing capacity of adult primate and human cardiomyocytes.     

Reproductive compensation in human populations

Reproductive compensation was studied in Russian (family planning) and Middle-Asian (with natural reproduction) urban and rural populations. Questionnaires were used describing postreproductive-age women having at least one pregnancy. The presence of reproductive compensation in a population was identified by comparison of two groups: "loaded" and "unloaded" by values of total and effective fertility. Families with excessive (compared with the mean population value) pregnancy outcome failure (spontaneous abortions, stillbirths, preproductive-age deaths of children) were ascribed to the loaded group. Reproductive compensation was discovered in all populations studied, which indicates that this phenomenon is wide-spread in human populations.     

Influence of different types of mineral fertilizers on reproduction of Listeria monocytogenes in soil

Influence of mineral fertilizers on the reproduction of Listeria monocytogenes in soil ecosystems under different temperatures (4-6 degrees C and 20-22 degrees C) was studied. Application of the fertilizers favored preservation and active reproduction of L. monocytogenes in brown podzolic soil and brown forest soil. Duration of application of the mineral fertilizers positively correlated with preservation and reproduction of L. monocytogenes in different types of soil.     

鱼类的繁殖类型

鱼类与高等脊椎动物相比其繁殖方式具有多样性,不仅有卵生、胎生和卵胎生,还有孤雌生殖、雌核发育和杂合发育。     

Genetic analysis for drought resistance of rice at reproductive stage in field with different types of soil

Drought resistance of rice is a complex trait and is mainly determined by mechanisms of drought avoidance and drought tolerance. The present study was conducted to characterize the genetic basis of drought resistance at reproductive stage in field by analyzing the QTLs for drought response index (DRI, normalized by potential yield and flowering time), relative yield, relative spikelet fertility, and four traits of plant water status and their relationships with root traits using a recombinant inbred population derived from a cross between an indica rice and upland rice. A total of 39 QTLs for these traits were detected with individual QTL explained 5.1–32.1% of phenotypic variation. Only two QTLs for plant water status were commonly detected in two environments, suggesting different mechanisms might exist in two types of soil conditions. DRI has no correlation with potential yield and flowering time under control, suggesting that it can be used as a good drought resistance index in field conditions. The co-location of QTLs for canopy temperature and delaying in flowering time suggested a usefulness of these two traits as indexes in drought resistance screening. Correlation and QTL congruence between root traits and putative drought tolerance traits revealed that drought avoidance (via thick and deep root traits) was the main genetic basis of drought resistance in sandy soil condition, while drought tolerance may play more role in the genetic basis of drought resistance in paddy soil condition. Therefore, both drought mechanisms and soil textures must be considered in the improvement of drought resistance at reproductive stage in rice.     

Transferrin types and reproduction in sheep

Transferrin types were determined for flocks of Finnish Landrace, Clun Forest, Soay and Merino sheep and gene frequencies were calculated. Analysis of ratios of transferrin types in segregating matings of Finnish Landrace and Clun Forest revealed a significant excess of heterozygotes in matings of heterozygous rams with heterozygous and with homozygous ewes. In Finnish Landrace, matings of sheep homozygous for Tf ^c to those heterozygous for Tf ^C gave a significant excess of homozygous male lambs and heterozygous female lambs. Finnish Landrace ewes of transferrin type BD had smaller litters than ewes of other types.     

Mechanisms of incomplete prezygotic reproductive isolation in an intertidal snail: testing behavioural models in wild populations

Two morphs (ecotypes) of the marine snail Littorina saxatilis coexist along Galician exposed rocky shores. They hybridize, but gene flow is impeded by a partial prezygotic reproductive barrier, and we have earlier suggested that this is a case of incipient sympatric speciation. To assess the mechanisms of prezygotic reproductive isolation, we estimated deviations from random mating (sexual selection and sexual isolation) of sympatric snails in 13 localities on the shore, and performed mate choice experiments in the laboratory. We also investigated the microdistribution of both morphs over patches of barnacles and blue mussels in the hybridization zone. We used computer simulations to separate the mechanisms contributing to reproductive isolation. On the shores sampled, male–female pairs were strongly assortative both with respect to morphs (mean Yule's V = 0.77) and size (mean Pearson's r = 0.47). In the laboratory, males of both morphs mounted other snails and mated other males and juveniles at random. However, mature females of equal sizes mated assortatively with respect to morph. The two morphs were nonrandomly distributed over barnacle and mussel patches in the hybridization zone. Monte Carlo simulations showed that this microdistribution could explain about half the morph and size relationships in male–female pairs, while a simple rejection mechanism, rejecting the first 1–3 mates if they were of contrasting morphs, accounted for the remaining part of the reproductive isolation, and for parts of the size relationships found between mates. A size discriminant mate choice mechanism may also, to a lesser extent, contribute to the sexual isolation. Sexual selection was observed for female size (larger ones being favoured) and among certain morphs, but distinct biological mechanisms may cause these processes.     

Classification of types of ontogenetic reproduction

The object of this paper is to present an original classification of ontogenetic reproduction. The main general criterion used is the degree and type of phylogenetic differentiation. In relation to this criterion, criteria are given for the classification of the fundamental types of ontogenetic reproduction and for the classification of the types of ontogenetic generation cycles. Between the fundamental types of ontogenetic reproduction and the types of ontogenetic generation cycles there is a hierarchical relationship which shows that the former are components of the latter. Between the well-defined types of ontogenetic reproduction there exist many intermediate types.     

Mechanisms in the regulation of the level of lipid radiosensitizing agents in yeast cells with different types of radioresistance

Factors controlling the lipid sensitizers level: the composition of fatty lipid acids, their antioxidative activity, the enzyme systems reactivity (superoxide dismutase, catalase, glutatione peroxidase and glutatione reductase) have been studied in yeast cells with different radioresistance. In six lines of yeast cells the leading role of superoxide dismutase--one of the regulators of lipid peroxidation have been demonstrated in cells native radioresistance formation.     

Genetic analysis of reproduction in the Buryat populations

A complex anthropological survey based on population-genetic methods and a study of a wide spectrum of genetic systems (43 alleles from 17 independent loci) was undertaken among 450 Buryat women of post-reproductive age. The results obtained showed the influence of particular genetic markers and their complex on the formation of peculiarities in the reproduction structure of the Buryat population.A sharp increase in phenotype GC 2-2 frequency and the corresponding GC*2 allele of the group-specific component (GC) was established for women groups with burdened obstetric records. These groups are characterized also by a considerable decrease in the observed geterozygosity (Ho) as compared to its expected value (He). Samples including women with multiple pregnancies in the recorded obstetric anamnesis are characterized by a significant increase in the frequency of the rare alleles TF*C3 of the transferrin system and those of PI*Z belonging to the proteinase inhibitor system (a1-antitrypsin) as compared to the control group.The results obtained widened current knowledge about the influence of genetic and environmental components on reproduction processes in human populations.     

The consequences of earlier reproduction in declining populations

Conflicting claims have been published concerning the consequences of earlier reproduction. In particular, it has been claimed that earlier reproduction will increase the rate of decline in a declining population, have no effect in a stable population, and enhance the rate of growth in an increasing population. However, if fecundity and mortality are conceptually separated so that earlier reproduction is defined as moving the fecundity column of the life table forward in time but not changing the mortality column, then earlier reproduction will nearly always cause the rate of change of a population to become more positive. This definition is believed to be more consistent with what biologists think of as earlier reproduction. Also, this concept requires that the cost of reproducing earlier be explicitly addressed rather than hiding it in assumptions implicit in a definition of earlier reproduction. This paper reconciles published mathematical demography models with published biological claims concerning earlier reproduction.     

Mechanisms of reproductive aging in the females

Aging is a developmental process occurring in all living organisms after reaching a critical developmental stage, characterized by progressive loss of functions until death. Different cells/tissues age differently depending on epigenetics and cell-cell interactions. While males maintain fertility for the most part of their life females only maintain reproductive ability for a short time compared with their lifespan. The interesting question is why and how the females lose fertility so quickly. There have been many hypotheses proposed from different perspectives and recent research has revealed unusual interactions between germ cells and somatic cells which may determine the lifespan of reproduction in the females. This review briefly discusses recent progress in reproductive aging in the well studied model, C. elegans, and focuses on the molecular mechanisms which may be conserved across all animals including humans.     

不同地理种群和红色及绿色麦长管蚜遗传多样性分析

麦长管蚜Sitobion avenae(Fabricius)体色变异(红色和绿色)是一种常见的生物学现象,揭示其体色的转换机制对该类害虫的防控和测报具有潜在意义。本文利用微卫星标记技术,对麦长管蚜种群进行聚类分析和分子方差分析,从群体遗传学角度研究了不同地理种群和不同色型之间遗传多样性差异。研究结果表明,麦长管蚜的遗传分化主要以种群内的变异为主,种群间的变异占总变异的比例很小。此外,研究发现,红、绿体色间的遗传分化并不显著,且存在频繁的基因交流。这说明不同区域的不同体色麦长管蚜种群各自之间具有相似的遗传背景。