Scholarly Literature

This is a database of scholarly literature that concentrates currently on natural and engineered selfish genetic elements (gene drives).  The latest are shown here.
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Evolution of driving X chromosomes and resistance factors in experimental populations of Drosophila simulans

4350
Capillon, CA, A.,  Evolution,  53:506-517. 1999-01-08 00:00:00.
Sex-ratio drive is a particular case of meiotic drive, described in several Drosophila species, that causes males bearing driving X chromosome to produce a large excess of females in their progeny. In Drosophila simulans, driving X chromosomes and resistance factors located on the Y chromosome and on the autosomes have been previously reported. In this paper, we report the study of the dynamics of sex-ratio factors in experimental populations. We followed the evolution in frequency of driving X chromosomes in the absence of resistance factors and the evolution of resistance factors in the presence of driving X chromosomes. The driving X chromosome was lost, contrarily to theoretical expectations that predict its rapid invasion. Autosomal resistances increased in frequency, and resistant Y chromosomes invaded the population very quickly, as predicted by theoretical models. Fitness measurements showed that the loss of the driving X chromosome was due to a strong deleterious effect that was expressed only when distorting males were in competition with standard males. However, the spread of autosomal resistances reduced this deleterious effect. Implications for the maintenance of polymorphism in natural populations are discussed.

Meiotic drive of chromosomal knobs reshaped the maize genome

4349
Buckler, ESP-D, T. L.; Buckler, C. S. K.; Dawe, R. K.; Doebley, J. F.; Holtsford, T. P.,  Genetics,  153:415-426. 1999-01-07 00:00:00.
Meiotic drive is the subversion of meiosis so that particular genes are preferentially transmitted to the progeny. Meiotic drive generally causes the preferential segregation of small regions of the genome; however, in maize we propose that meiotic drive is responsible for the evolution of large repetitive DNA arrays on all chromosomes. A maize meiotic drive locus found on an uncommon form of chromosome 10 [abnormal 10 (Ab10)] may be largely responsible for the evolution of heterochromatic chromosomal knobs, which can confer meiotic drive potential to every maize chromosome. Simulations were used to illustrate the dynamics of this meiotic drive model and suggest knobs might be deleterious in the absence of Ab10. Chromosomal knob data from maize's wild relatives (Zea mays ssp. parviglumis and mexicana) and phylogenetic comparisons demonstrated that the evolution of knob size, frequency, and chromosomal position agreed with the meiotic drive hypothesis. Knob chromosomal position was incompatible with the hypothesis that knob repetitive DNA is neutral or slightly deleterious to the genome. We also show iv that environmental factors and transposition may play a role in the evolution of knobs. Because knobs occur at multiple locations on all maize chromosomes, the combined effects of meiotic drive and genetic linkage may have reshaped genetic diversity throughout the maize genome in response to the presence of Ab10. Meiotic drive may be a major force of genome evolution, allowing revolutionary changes in genome structure and diversity over short evolutionary periods.

Segregation distortion in a deme structured population: opposing demands of gene, individual and group selection

4364
van Boven, MW, F. J.,  Journal of Evolutionary Biology,  12:80-93. 1999-01-02 00:00:00.
The evolution of segregation distortion is governed by the interplay of selection at different levels. Despite their systematic advantage at the gamete level, none of the well-known segregation distorters spreads to fixation since they induce severe negative fitness effects at the individual level. In a deme-structured population, selection at the population level also plays a role. By means of a population genetical model, we analyse the various factors that determine the success of a segregation distorter in a metapopulation, Our focus is on the question of how the success of a distorter allele is affected by its segregation ratio and its fitness effects at the individual level. The analysis reveals that distorter alleles with high segregation ratios are the best invaders and reach the highest frequencies within single demes. However, the productivity of a deme harbouring a distorter with a high segregation ratio may be significantly reduced. As a consequence, an efficient distorter will be underrepresented in the migrant pool and, moreover, it may increase the probability of deme extinction. In other words, efficient distorters with high segregation ratios may well succumb to their own success. Therefore, distorters with intermediate segregation ratios may reach the highest frequency in the metapopulation as a result of the opposing forces of gamete, individual and group selection. We discuss the implications of this conclusion for the t complex of the house mouse.

Mariner transposition and transformation of the yellow fever mosquito, Aedes aegypti

6256
C. J. Coates, N. Jasinskiene, L. Miyashiro and A. A. James,  Proceedings of the National Academy of Sciences of the United States of America,  95:3748-3751. 1998-03-07 19:31:51.
The mariner transposable element is capable of interplasmid transposition in the embryonic soma of the yellow fever mosquito, Aedes aegypti. To determine if this demonstrated mobility could be utilized to genetically transform the mosquito, a modified mariner element marked with a wild type allele of the Drosophila melanogaster cinnabar gene was microinjected into embryos of a kynurenine hydroxylase-deficient, white-eyed recipient strain. Three of 69 fertile male founders resulting from the microinjected embryos produced families with colored-eyed progeny individuals, a transformation rate of 4%. The transgene-mediated complementation of eve color was observed to segregate in a Mendelian manner, although one insertion segregates with the recessive allele (female-determining) of the sex-determining locus, and a separate insertion is homozygous lethal. Molecular analysis of selected transformed families demonstrated that a single complete copy of the construct had integrated independently in each case acid that it had done so in a transposase-mediated manner. The availability of a mariner transformation system greatly enhances our ability to study and manipulate this important vector species.

Stable transformation of the yellow fever mosquito, Aedes aegypti, with the Hermes element from the housefly

6254
N. Jasinskiene, C. J. Coates, M. Q. Benedict, A. J. Cornel, C. S. Rafferty, A. A. James and F. H. Collins,  Proceedings of the National Academy of Sciences of the United States of America,  95:3743-3747. 1998-03-07 19:28:29.
The mosquito Aedes aegypti is the world's most important vector of yellow fever and dengue viruses, Work is currently in progress to control the transmission of these viruses by genetically altering the capacity of wild Ae, aegypti populations to support virus replication. The germ-line transformation system reported here constitutes a major advance toward the implementation of this control strategy, A modified Hermes transposon carrying a 4.7-kb fragment of genomic DNA that includes a wild-type allele of the Drosophila melanogaster cinnabar (cn) gene was used to transform a white-eyed recipient strain of Ae, aegypti. Microinfection of preblastoderm mosquito embryos with this construct resulted in 50% of the emergent G(0) adults showing some color in their eyes, Three transformed families were recovered, each resulting from an independent insertion event of the cn(+)-carrying transposon, The cn(+) gene functioned as a semidominant transgene and segregated in Mendelian ratios, Hermes shows great promise as a vector for efficient, heritable, and stable transformation of this important mosquito vector species.

Meiotic drive favors Robertsonian metacentric chromosomes in the common shrew (Sorex araneus, Insectivora, Mammalia)

4380
Wyttenbach, AB, P.; Hausser, J.,  Cytogenetics and Cell Genetics,  83:199-206. 1998-01-18 00:00:00.
Meiotic drive has attracted much interest because it concerns the robustness of Mendelian segregation and its genetic and evolutionary stability. We studied chromosomal meiotic drive in the common shrew (Sorex araneus, Insectivora, Mammalia), which exhibits one of the most remarkable chromosomal polymorphisms within mammalian species. The open question of the evolutionary success of metacentric chromosomes (Robertsonian fusions) versus acrocentrics in the common shrew prompted us to test whether a segregation distortion in favor of metacentrics is present in female and/or male meiosis. Performing crosses under controlled laboratory conditions with animals from natural populations, we found a clear trend toward a segregation distortion in favor of metacentrics during male meiosis, two chromosome combinations (gm and ji) being significantly preferred over their acrocentric homologs. Apart for one Robertsonian fusion (hi), this trend was absent in female meiosis. We propose a model based on recombination events between twin acrocentrics to explain the difference in transmission ratios of the same metacentric in different sexes and unequal drive of particular metacentrics in the same sex. Pooled data for female and male meiosis revealed a trend toward stronger segregation distortion for larger metacentrics. This is partially in agreement with the frequency of metacentrics occurring in natural populations of a chromosome race showing a high degree of chromosomal polymorphism.

Male eye span in stalk-eyed flies indicates genetic quality by meiotic drive suppression

4379
Wilkinson, GSP, D. C.; Crymes, L.,  Nature,  391:276-279. 1998-01-17 00:00:00.
In some species, females choose mates possessing ornaments that predict offspring survival(1-5). However, sexual selection by female preference for male genetic quality(6-8) remains controversial because conventional genetic mechanisms maintain insufficient variation in male quality to account for costly preference and ornament evolution(9,10). Here we show that females prefer ornaments that indicate genetic quality generated by transmission conflict between the sex chromosomes, By comparing sex-ratio distributions in stalk-eyed fly (Cyrtodiopsis) progeny we found that female-biased sex ratios occur in species exhibiting eye-stalk sexual dimorphism(11,12) and female preferences for long eye span(13,14). Female-biased sex ratios result from meiotic drive(15), the preferential transmission of a 'selfish' X-chromosome. Artificial selection for 22 generations on male eye-stalk length in sexually dimorphic C. dalmanni produced longer eye-stalks and male-biased progeny sex ratios in replicate lines. Because male-biased progeny sex ratios occur when a drive-resistant Y chromosome pairs with a driving X chromosome(15), long eye span is genetically linked to meiotic drive: suppression. Male eye span therefore signals genetic quality by influencing the reproductive value of offspring(16).

Sex determination, sex ratios, and genetic conflict

4378
Werren, JHB, L. W.,  Annual Review of Ecology and Systematics,  29:233-261. 1998-01-16 00:00:00.
Genetic mechanisms of sex determination are unexpectedly diverse and change rapidly during evolution. We review the role of genetic conflict as the driving force behind this diversity and turnover. Genetic conflict occurs when different components of a genetic system are subject to selection in opposite directions. Conflict may occur between genomes (including paternal-maternal and parental-zygotic conflicts) or within genomes (between cytoplasmic and nuclear genes or sex chromosomes and autosomes). The sex-determining system consists of parental sex-ratio genes, parental-effect sex determiners, and zygotic sex determiners, which are subject to different selection pressures because of differences in their modes of inheritance and expression. Genetic conflict theory is used to explain the evolution of several sex-determining mechanisms, including sex chromosome drive, cytoplasmic sex-ratio distortion, and cytoplasmic male sterility in plants. Although still limited, there is growing evidence that genetic conflict could be important in the evolution of sex-determining mechanisms.

Evolution of segregation distortion: Potential for a high degree of polymorphism

4377
van Boven, MW, F. J.,  Journal of Theoretical Biology,  192:131-142. 1998-01-15 00:00:00.
By means of a population genetical model, we study the evolution of segregation distortion. Most models of segregation distortion focus on a single distorter allele. In contrast, we consider the competition between a large number of distorters. Motivated by systems as the t complex of the house mouse or the Sd complex of Drosophila melanogaster, we assume that there is some "complementation" between distorter alleles, i.e. that the fitness of individuals heterozygous for two distorter alleles is higher than the fitness of homozygous individuals. In the presence of complementation, the most efficient distorter allele with the highest segregation ratio often does not outcompete less efficient distorters. In fact, our results show that coexistence of a large number of distorter alleles is more typical than the competitive exclusion of less efficient distorters by a single superior allele. We first consider the analytically tractable system where all distorters show the same amount of complementation. In this case, all distorters with a segregation ratio higher than a certain critical value will persist, resulting in a polymorphic population where the average segregation ratio is only slightly larger than 0.5. If the degree of complementation varies, there may be more than one stable equilibrium, and the outcome of competition may depend on the initial conditions. Motivated by empirical examples, we also consider the case that the distorting ability of an allele is negatively related to its effects on individual fitness. Interestingly, the outcome of competition depends crucially on details of such a trade-off. We conclude that verbal arguments are insufficient to predict the evolution of segregation distortion. (C) 1998 Academic Press Limited.

The dynamics of maternal-effect selfish genetic elements

4376
Smith, NGC,  Journal of Theoretical Biology,  191:173-180. 1998-01-14 00:00:00.
Maternal-effect selfish genes such as Medea or Seat act to kill progeny that do not bear a copy of the selfish gene present in the mother. Previous models of this system allowed for two types of allele, the selfish (killer) type and the sensitive (susceptible) wild-type. These models predict that the invasion conditions of the selfish allele are quite broad and that if invasion is possible a high frequency equilibrium is to be expected. The selfish element is therefore predicted to persist. Here a hypothetical third allele that neither kills nor is killed (i.e, insensitive) is considered. Such an allele could enter a population by recombination, mutation or migration. The incorporation of this third allele profoundly affects the dynamics of the system and, under some parameter values, it is possible for the spread of the insensitive allele to lead, eventually, to the fixation of the wild-type allele (reversible evolution). This is most likely if the death of progeny provides no direct benefit to the surviving sibs (i.e. in the absence of fitness compensation), as in insects without gregarious broods. Under these circumstances the selfish element cannot spread when infinitely rare, only after having risen to some finite frequency. A fitness cost to bearing the killer allele then causes its loss. However, if fitness compensation is found (e.g, in placental mammals) the invasion of the selfish element from an infinitely low level is possible for a wide range of costs and both stable coexistences of all three alleles and limit cycles of all three are then found. It is therefore to be expected that in mammals selfish maternal-effect genes are more likely both to spread and to persist than in insects, due to their different levels of fitness compensation. (C) 1998 Academic Press Limited.

Male sterility and meiotic drive associated with sex chromosome rearrangements in Drosophila: Role of X-Y pairing

4375
McKee, BDW, K.; Merrill, C.; Ren, X. J.,  Genetics,  149:143-155. 1998-01-13 00:00:00.
In Drosophila melanogaster, deletions of the pericentromeric X heterochromatin cause X-Y nondisjunction, reduced male fertility and distorted sperm recovery ratios (meiotic drive) in combination with a normal Y chromosome and interact with Y-autosome translocations (T(Y;A)) to cause complete male sterility. The pericentromeric heterochromatin has been shown to contain the male-specific X-Y meiotic pairing sites, which consist mostly of a 240-bp repeated sequence in the intergenic spacers (IGS) of the rDNA repeats. The experiments in this paper address the relationship between X-Y pairing failure and the meiotic drive and sterility effects of Xh deletions. X-linked insertions either of complete rDNA repeats or of rDNA fragments that contain the IGS were found to suppress X-Y nondisjunction and meiotic drive in Xh(-)/Y males, and to restore fertility to Xh(-)/T(Y;A) males for eight of nine tested Y-autosome translocations. rDNA fragments devoid of IGS repeats proved incapable of suppressing either meiotic drive or chromosomal sterility. These results indicate that the various spermatogenic disruptions associated with X heterochromatic deletions are all consequences of X-Y pairing failure. We interpret these findings in terms of a novel model in which misalignment of chromosomes triggers a checkpoint that acts by disabling the spermatids that derive from affected spermatocytes.

Segregation distortion in myotonic dystrophy

4374
Magee, ACH, A. E.,  Journal of Medical Genetics,  35:1045-1046. 1998-01-12 00:00:00.
Myotonic dystrophy (DM) is an autosomal dominant disease which, in the typical pedigree, shows a three generation anticipation cascade. This results in infertility and congenital myotonic dystrophy (CDM) with the disappearance of DM in that pedigree. The concept of segregation distortion, where there is preferential transmission of the larger allele at the DM locus, has been put forward to explain partially the maintenance of DIM in the population. In a survey of DM in Northern Ireland, 59 pedigrees were ascertained. Sibships where the status of all the members had been identified were examined to determine the transmission of the DM expansion from affected parents to their offspring. Where the transmitting parent was male, 58.3% of the offspring were affected, and in the case of a female transmitting parent, 68.7% were affected. Studies on meiotic drive in DIM have shown increased transmission of the larger allele at the DM locus in non-DIM heterozygotes for CTGn. This study provides further evidence that the DM expansion tends to be transmitted preferentially.

Sex ratio distortion in Acraea encedon (Lepidoptera : Nymphalidae) is caused by a male-killing bacterium

4373
Jiggins, FMH, G. D. D.; Majerus, M. E. N.,  Heredity,  81:87-91. 1998-01-11 00:00:00.
Females of the butterfly Acraea encedon produce either entirely female offspring or males and females in an almost 1:1 sex ratio. The sex ratio produced is maternally inherited and was previously attributed to sex chromosome meiotic drive. We report that all-female lineages are associated with low egg-hatching rates and that the trait is cured by antibiotic treatment. We thus reject the hypothesis that this sex ratio bias is caused by a meiotically driven sex chromosome and, instead, propose that it is associated with a maternally inherited bacterium that kills males.

Selfish genes and meiotic drive

4372
Hurst, LD,  Nature,  391:223-223. 1998-01-10 00:00:00.
Work by Gerald Wilkinson and colleagues3 on stalk-eyed flies (Diopsidae), described on page 276, provides the strongest evidence to date about the nature of some of the genes females prefer. As their name suggests, stalk-eyed flies have their eyes perched on the end of side-projecting stalks (see the cover of this issue). These can reach ridiculous proportions. In two of the species studied, males have considerably greater eye span than females, and male eye span even exceeds body length. In both of these species females show a strong preference for males with a large eye span. In a third species, male eye span was much shorter (indeed no different to female eye span) and there was no female choice.

Selfish genetic elements and speciation

4371
Hurst, GDDS, M.,  Heredity,  80:2-8. 1998-01-09 00:00:00.
This review concerns the importance of selfish genetic elements (SGEs) in speciation. We assess the importance of medea genes, meiotic drive elements, transposable elements and the bacterium Wolbachia in the creation of postzygotic isolation. Although all of these elements can contribute to postzygotic isolation, their contribution will often disappear if there is gene flow between the populations. Further, there is the possibility that incompatibilities produced by SGEs may lessen over time. We conclude that although some of the case studies are tantalizing, particularly those associated with Wolbachia, the role of selfish genetic elements in speciation remains unproven.

Identification of the t complex-encoded cytoplasmic dynein light chain Tctex1 in inner arm I1 supports the involvement of flagellar dyneins in meiotic drive

4370
Harrison, AO-C, P.; King, S. M.,  Journal of Cell Biology,  140:1137-1147. 1998-01-08 00:00:00.
The cytoplasmic dynein light chain Tctex1 is a candidate for one of the distorter products involved in the non-Mendelian transmission of mouse t haplotypes. It has been unclear, however, how the t-specific mutations in this protein, which is found associated with cytoplasmic dynein in many tissues, could result in a male germ cell-specific phenotype. Here, we demonstrate that Tctex1 is not only a cytoplasmic dynein component, but is also present both in mouse sperm and Chlamydomonas flagella. Genetic and biochemical dissection of the Chlamydomonas flagellum reveal that Tctex1 is a previously undescribed component of inner dynein arm Il. Combined with the recent identification of another putative t complex distorter, Tctex2, within the outer dynein arm, these results support the hypothesis that transmission ratio distortion (meiotic drive) of mouse t haplotypes involves dysfunction of both flagellar inner and outer dynein arms but does not require the cytoplasmic isozyme.

Malaria: existing methods of vector control and molecular entomology

4369
Curtis, CFT, H.,  British Medical Bulletin,  54:311-325. 1998-01-07 00:00:00.
In general, the most effective means of malaria vector control is the killing of adult mosquitoes with a residual insecticide applied to bednets or sprayed on house walls and ceilings. Major reductions in all-cause child mortality have been achieved in Africa by these means. In some circumstances, personal protection and larval control may also make a contribution. We discuss the prospects of genetic control by release of sterile male mosquitoes or driving genes for refractoriness to malaria into wild populations. Many major malaria vectors belong to complexes of sibling species which differ in vectorial and biological characteristics. Distinguishing the species by cytogenetic or molecular methods is important for epidemiological studies and could improve the targeting of control.

Wolbachia as a possible means of driving genes into populations

4368
Curtis, CFS, S. P.,  Parasitology,  116:S111-S115. 1998-01-06 00:00:00.
Cytoplasmic incompatibility consists of sterility in cross matings, the crossing type being maternally inherited. It can be explained by the action of Wolbachia symbionts which are transmitted through the egg cytoplasm and leave an imprint on the sperm which prevents it fertilizing unless it is 'rescued' by the action of the same type of Wolbachia in the egg. Thus matings between infected males and uninfected females are sterile, but the reciprocal matings are fertile. Hence uninfected females are at risk of failing to transmit their uninfected cytoplasm if they cross mate, but infected females are at no such risk. Therefore natural selection favours the infected state and in two wild insect populations the infection has been observed spreading. If a gene for inability to transmit malaria could be introduced into Wolbachia and if this could be introduced into Anopheles (where these symbionts appear not to occur naturally), release of a limited number of such insects should trigger a process of displacement of malaria vectors, by the non-vector type. A simple model is used to demonstrate the limitations to this process which would be introduced by immigration.

Localization of the genes controlling B chromosome transmission rate in maize (Zea mays ssp. mays, Poaceae)

4367
Chiavarino, AMR, M.; Rosi, P.; Poggio, L.; Naranjo, C. A.,  American Journal of Botany,  85:1581-1585. 1998-01-05 00:00:00.
In previous papers we found that the frequency of B chromosomes in native races of maize varies considerably in different populations. Moreover, we found genotypes that control high and low transmission rates (TR) of B chromosomes in the Pisingallo race. In the present work crosses were made to determine whether the genes controlling B-TR are located on the normal chromosome set (As) or on the B chromosomes (Bs). We made female f.0B X male m.2B crosses between and within high (H) and low (L) B-TR groups. The Bs were transmitted on the male side in all cases. The mean B-TR from the progeny of f.0B (H) X m.2B (H) and f.0B (H) X m.2B (L) crosses was significantly higher than that from f.0B (L) X m.2B (L) and f.0B (L) X m.2B (H) crosses. The results show that the B-TR of the crosses corresponds to the H or L B-TR of the 0B female parents irrespective of the Bs of the male parent. This indicates that B-TR is genetically controlled by the 0B female parent and that these genes are located on the A chromosomes.

Selfish DNA and breeding system in flowering plants

4366
Burt, AT, R.,  Proceedings of the Royal Society B-Biological Sciences,  265:141-146. 1998-01-04 00:00:00.
In many species, some individuals carry one or more B chromosomes: extra, or supernumerary chromosomes not part of the normal complement. In most well-studied cases, B's lower the fitness of their carrier and persist in populations only because of accumulation mechanisms analogous to meiotic drive. It has been suggested that such genomic parasites are expected to persist only in outcrossed sexual species, in which uninfected lines of descent can be continuously reinfected; in inbred or asexual species, all selection is between lines of descent, and the genomic parasites are either lost or must evolve into commensals or mutualists. Here we present a simple population genetic model of the effect of outcrossing rate on the frequency of B chromosomes, and find that outcrossing facilitates the spread of parasitic B's, but inhibits the spread of mutualists. Data compiled from the literature on breeding system and B chromosomes of British plants indicate that B's are much more likely to be reported from obligately outcrossed species than inbred species. These results support the ideas that most B chromosomes are parasitic, and that breeding systems play a central role in the biology of selfish genes.

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