A selfish DNA element engages a meiosis-specific motor and telomeres for germ-line propagation

The chromosome-like mitotic stability of the yeast 2 micron plasmid is conferred by the plasmid proteins Rep1-Rep2 and the cis-acting locus STB, likely by promoting plasmid-chromosome association and segregation by hitchhiking. Our analysis reveals that stable plasmid segregation during meiosis requires the bouquet proteins Ndj1 and Csm4. Plasmid relocalization from the nuclear interior in mitotic cells to the periphery at or proximal to telomeres rises from early meiosis to pachytene. Analogous to chromosomes, the plasmid undergoes Csm4- and Ndj1-dependent rapid prophase movements with speeds comparable to those of telomeres. Lack of Ndj1 partially disrupts plasmid–telomere association without affecting plasmid colocalization with the telomere-binding protein Rap1. The plasmid appears to engage a meiosis-specific motor that orchestrates telomere-led chromosome movements for its telomere-associated segregation during meiosis I. This hitherto uncharacterized mode of germ-line transmission by a selfish genetic element signifies a mechanistic variation within the shared theme of chromosome-coupled plasmid segregation during mitosis and meiosis.     

A selfish origin for recombination

Recent findings of molecular biology show that recombination is initiated by interactions between homologous chromosomes and that an allele can induce the initiation of recombination on the homolog. Since gene conversion at the site of initiation is strong enough to promote the transmission of that allele, recombination may be a way for a self-promoting element to spread, even if it gives no advantage to the individual or to the population. I develop a simple model and discuss available molecular evidence in support of this hypothesis. A consequent argument is that with asexual reproduction the evolution of recombination leads to an intragenomic conflict, and a possible outcome of this conflict may be the origin of sexual reproduction.     

The yeast 2 micron plasmid: strategies for the survival of a selfish DNA

Summary The designation of the yeast 2 circle as a selfish DNA molecule has been confirmed by demonstrating that the plasmid is lost with exponential kinetics from haploid yeast populations grown in continuous culture. We show that plasmid-free yeast cells have a growth rate advantage of some 1.5%–3% over their plasmid-containing counterparts. This finding makes the ubiquity of this selfish DNA in yeast strains puzzling. Two other factors probably account for its survival. First, the rate of plasmid loss was reduced by allowing haploid populations to enter stationary phase periodically. Second, it was not possible to isolate a plasmid-free segregant from a diploid yeast strain. Competition experiments demonstrated that stability in a diploid is conferred at the level of segregation and that plasmid-free diploid cells are at a selective advantage compared with their plasmid-containing counterparts. Yeast cells in nature are usually homothallic and must frequently pass through both diploid and stationary phases. The 2 plasmid appears to have evolved a survival strategy which exploits these two features of its host's life cycle.     

Heterochromatin of the human Y chromosome as an example of selfish DNA

The nature of human Y-chromosome of Q-positive heterochromatic region is discussed. Both the authors data and those from literature show the existence of human population polymorphism with respect to the appearance of this region which consists of one or several bright fluorescent blocks. Their multiplication results probably from an unequal sister-strand crossing-over. Absence of these blocks has no visible phenotypic effect. Their extra multiplication affects the embryonal and possibly postnatal psychic development. It is supposed that Q-positive heterochromatin is an example of selfish DNA in the human genome.     

Altruistic Behavior among Twins

According to kin selection theory, indirect reproductive advantages may induce individuals to care for others with whom they share genes by common descent, and the amount of care, including self-sacrifice, will increase with the proportion of genes shared. Twins represent a natural situation in which this hypothesis can be tested. Twin pairs experience the same early environment because they were born and raised at the same time and in the same family but their genetic relatedness differs depending on zygosity. We compared the degree of willingness to fight and sacrifice for the co-twin among monozygotic (MZ) and dizygotic (DZ) pairs in a sample of 1443 same-sex and opposite-sex twins. We also analyzed the effect of the subject’s gender and that of the co-twin on those altruistic behaviors. Results partly supported the postulated explanation. MZ twins (who share nearly their entire genome) were significantly more likely than DZ twins (who on average share half of their segregating genes) to self-sacrifice for their co-twins, but zygosity did not affect willingness to fight for him/her. The genders of the subject and of the co-twin, not genetic relatedness, were the best predictors of aggressive altruistic intentions.     

Social insects and selfish genes

Sometimes science advances because of a new idea. Sometimes, it's because of a new technique. When both occur together, exciting times result. In the study of social insects, DNA-based methods for measuring relatedness now allow increasingly detailed tests of Hamilton's theory of kin selection.     

The struggle for life of the genome's selfish architects

Abstract  

Transposable elements (TEs) were first discovered more than 50 years ago, but were totally ignored for a long time. Over the last few decades they have gradually attracted increasing interest from research scientists. Initially they were viewed as totally marginal and anecdotic, but TEs have been revealed as potentially harmful parasitic entities, ubiquitous in genomes, and finally as unavoidable actors in the diversity, structure, and evolution of the genome. Since Darwin's theory of evolution, and the progress of molecular biology, transposable elements may be the discovery that has most influenced our vision of (genome) evolution. In this review, we provide a synopsis of what is known about the complex interactions that exist between transposable elements and the host genome. Numerous examples of these interactions are provided, first from the standpoint of the genome, and then from that of the transposable elements. We also explore the evolutionary aspects of TEs in the light of post-Darwinian theories of evolution.     

State-dependent foraging rules for social animals in selfish herds

Many animals gain benefits from living in groups, such as a dilution in predation risk when they are closely aggregated (referred to as the 'selfish herd'). Game theory has been used to predict many properties of groups (such as the expected group size), but little is known about the proximate mechanisms by which animals achieve these predicted properties. We explore a possible proximate mechanism using a spatially explicit, individual-based model, where individuals can choose to rest or forage on the basis of a rule-of-thumb that is dependent upon both their energetic reserves and the presence and actions of neighbours. The resulting behaviour and energetic reserves of individuals, and the resulting group sizes, are shown to be affected both by the ability of the forager to detect conspecifics and areas of the environment suitable for foraging, and by the distribution of energy in the environment. The model also demonstrates that if animals are able to choose (based upon their energetic reserves) between selecting the best foraging sites available and moving towards their neighbours for safety, then this also has significant effects upon individuals and group sizes. The implications of the proposed rule-of-thumb are discussed.     

Revising the selfish DNA hypothesis: new evidence on accumulation of transposable elements in heterochromatin

The bulk of the eukaryotic genome is composed of families of repetitive sequences that are genetically silent and exhibit various types of instability. Transposable elements (TEs) are particularly common in heterochromatic regions of the genome - a location where TEs might do less damage to their host. Recent advances suggest that the relationship between TEs and heterochromatin might not be quite so straightforward.     

Altruistic surrogacy and informed consent

A crucial premise in many recent arguments against the moral permissibility of surrogate motherhood arrangements is the claim that a woman cannot autonomously consent to gestating and relinquishing a child to another couple, because she cannot be fully informed about what her future emotional responses will be to the foetus developing within her, and to the giving up of the newborn infant to its social parents. When conjoined with some moral principle about the justifiable limits on the ways others can be expected to exercise their autonomy on our behalf, this claim is often taken to establish that various forms of surrogate motherhood arrangements are morally wrong. In this paper I want to show that there is a serious non sequitur in this kind of argument. That is, I want to show that even if women cannot in fact have this kind of information about what their future emotional responses to pregnancy and relinquishment will be, nothing follows about the wrongness or otherwise of surrogacy. For, when we consider what counts as informed consent in the context of other important ventures with uncertain consequences, it becomes clear that informed consent does not require having this kind of information about one's future emotional states. In putting these arguments, I also hope to clarify some of the connections which might be thought to hold between informed consent and autonomous decision-making generally.     

Multiple functions of DNA polymerases

The primary role of DNA polymerases is to accurately and efficiently replicate the genome in order to ensure the maintenance of the genetic information and its faithful transmission through generations. This is not a simple task considering the size of the genome and its constant exposure to endogenous and environmental DNA damaging agents. Thus, a number of DNA repair pathways operate in cells to protect the integrity of the genome. In addition to their role in replication, DNA polymerases play a central role in most of these pathways. Given the multitude and the complexity of DNA transactions that depend on DNA polymerase activity, it is not surprising that cells in all organisms contain multiple highly specialized DNA polymerases, the majority of which have only recently been discovered. Five DNA polymerases are now recognized in Escherichia coli, 8 in Saccharomyces cerevisiae, and at least 15 in humans. While polymerases in bacteria, yeast and mammalian cells have been extensively studied much less is known about their counterparts in plants. For example, the plant model organism Arabidopsis thaliana is thought to contain 12 DNA polymerases, whose functions are mostly unknown. Here we review the properties and functions of DNA polymerases focusing on yeast and mammalian cells but paying special attention to the plant enzymes and the special circumstances of replication and repair in plant cells.     

Altruistic Punishment and Between-Group Competition

Collective action, or the large-scale cooperation in the pursuit of public goods, has been suggested to have evolved through cultural group selection. Previous research suggests that the costly punishment of group members who do not contribute to public goods plays an important role in the resolution of collective action dilemmas. If large-scale cooperation sustained by the punishment of defectors has evolved through the mechanism of cultural group selection, two implications regarding costly punishment follow: (1) that people are more willing to punish defecting group members in a situation of intergroup competition than in a single-group social dilemma game and (2) that levels of "perverse" punishment of cooperators are not affected by intergroup competition. We find confirmation for these hypotheses. However, we find that the effect of intergroup competition on the punishment of defectors is fully explained by the stronger conditionality of punishment on expected punishment levels in the competition condition.