Evolutionary mysteries in meiosis

Lenormand, Thomas; Engelstädter, Jan; Johnston, Susan E.; Wijnker, Erik; Haag, Christoph R.

doi:10.1098/rstb.2016.0001

Cited by 119 publications

(127 citation statements)

References 191 publications

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“…Several mechanisms that maintain heterozygosity with little or no recombination may contribute to the longevity of asexual clades [3, 11]. Successful asexual lineages commonly generate heterozygous progeny either by skipping Meiosis I or by fusing two genetically distinct meiotic products (“central fusion”).…”

Section: Introductionmentioning

confidence: 99%

Genome Architecture and Evolution of a Unichromosomal Asexual Nematode

et al. 2017

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SUMMARY Asexual reproduction in animals, though rare, is the main or exclusive mode of reproduction in some long-lived lineages. The longevity of asexual clades may be correlated with the maintenance of heterozygosity by mechanisms that rearrange genomes and reduce recombination. Asexual species thus provide an opportunity to gain insight into the relationship between molecular changes, genome architecture and cellular processes. Here, we report the genome sequence of the parthenogenetic nematode Diploscapter pachys with only one chromosome pair. We show that this unichromosomal architecture is shared by a long-lived clade of asexual nematodes closely related to the genetic model organism Caenorhabditis elegans. Analysis of the genome assembly reveals that the unitary chromosome arose through fusion of six ancestral chromosomes, with extensive rearrangement among neighboring regions. Typical nematode telomeres and telomeric protection-encoding genes are lacking. Most regions show significant heterozygosity; homozygosity is largely concentrated to one region and attributed to gene conversion. Cell-biological and molecular evidence are consistent with the absence of key features of Meiosis I, including synapsis and recombination. We propose that D. pachys preserves heterozygosity and produces diploid embryos without fertilizationthrough a truncated meiosis. As a prelude to functional studies, we demonstrate that D. pachys is amenable to experimental manipulation by RNA interference.

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Section: Introductionmentioning

confidence: 99%

Genome Architecture and Evolution of a Unichromosomal Asexual Nematode

et al. 2017

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“…To address this, we included gene conversion on the regulatory region, on the gene, or on both. Apart from the fact that conversion on genes versus regulatory regions may have varying dynamical effects in our model, there is strong empirical evidence indicating that rates of recombination/conversion may markedly differ in these regions (Lenormand et al 2016). For simplicity, we assume that when conversion occurs at a locus, the individual becomes homozygous for one of its (randomly chosen) alleles.…”

Section: Reproductive Modesmentioning

confidence: 99%

“…Rates of gene conversion are usually quite low, c.a. 10 −5 (Gay et al 2007), but also heterogeneous within genomes, and possibly more frequent in regulatory regions than in genes for many eukaryotes, depending on hotspot location (Lenormand et al 2016).…”

Section: Clonal Lineagesmentioning

confidence: 99%

Cis-regulator runaway and divergence in asexuals

Fyon

Lenormand

2018

Evolution

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With the advent of new sequencing technologies, the evolution of gene expression is becoming a subject of intensive genomic research, with sparking debates upon the role played by these kinds of changes in adaptive evolution and speciation. In this article, we model expression evolution in species differing by their reproductive systems. We consider different rates of sexual versus asexual reproduction and the different type of parthenogenesis (apomixis and the various modes of automixis). We show that competition for expression leads to two selective processes on cis-regulatory regions that act independently to organism-level adaptation. Coevolution within regulatory networks allows these processes to occur without strongly modifying expression levels. First, cis-regulatory regions such as enhancers evolve in a runaway fashion because they automatically become associated to chromosomes purged from deleterious mutations ("Enhancer Runaway process"). Second, in clonal or nearly clonal species, homologous cis-regulatory regions tend to diverge, which leads to haploidization of expression, when they are sufficiently isolated from one another ("Enhancer Divergence process"). We show how these two processes cooccur and vary depending on the level of outcrossing, gene conversion, mitotic recombination, or recombination in automictic species. This study offers thus a baseline to understand patterns of expression evolution across the diversity of eukaryotic species.

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“…The topics addressed in this special issue range from very fundamental questions such as the evolutionary benefits [12] and the origin of sex [3,4,13] and mating types [6], to secondary consequences of sexual reproduction, such as sexual selection [5,11] and the increased scope for genetic conflict [8,10,14], and the cost of sex, either due to the production of males in anisogamous species or due to mate finding or mechanisms of meiosis [15].…”

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confidence: 99%

Weird sex: the underappreciated diversity of sexual reproduction

Aanen¹,

Beekman

Kokko

2016

Phil. Trans. R. Soc. B

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The idea for this project started over lunch in an Italian restaurant in Copenhagen in 2010. We were not planning to talk about sex at that time, but to discuss the evolution of uniparental inheritance. But as they say, one thing leads to another, and we started to talk about sex and its underappreciated weirdness. And the need for a project like this. Along the way, we were continuously reminded of the importance of such a project: the most recent example was a comment in an undergraduate 'learning diary', a teaching tool in which students are asked to explain hard to understand concepts, or concepts that are surprising to them. The student expressed great surprise to hear that vertebrate sex determination does not always follow the 'normal' XY pattern; in birds, sex is instead determined by ZW chromosomes and females are the heterogametic sex. Well, we thought, if ZW sex determination seems 'weird', then you ain't seen nothing yet!The student of course was not stupid, merely rather uninformed-or better put: biased in the same way we all tend to begin our careers as biologists. Our academic forays in sex and sexual selection start by learning that there are primary and secondary sexual characteristics, that these differences are caused by sex chromosomes, packaged in different kinds of gametes that need to come together by one type of gamete (sperm) finding the other (egg) via mostly internal fertilization. Only later might we realize that sex determination mechanisms are so diverse they deserve an entire book [1]. If we then retain our interest, at some point we learn, to our surprise, that monogamy is a really unusual reproductive system, and that sex itself isn't a self-evident feature of all reproduction. Even more so, sexual reproduction is a contradictio in terminis, since sex, in its very essence, involves fusion of gametes, thus reducing numbers instead of increasing numbers. The very existence and persistence of sexual reproduction remains an evolutionary puzzle.The list goes on. Selfing is common in plants, while more than a few animals also appear to have no objection to self-fertilization. Similarly, most evolutionary biologists are surprised when they learn that hermaphroditism in animals is actually rather widespread: close to 30% of all species are hermaphrodites [2]. Most plants do not have separate sexes, while the notion of 'maleness' and 'femaleness' becomes something rather different when one includes fungi and unicellular life. Slowly then, as we learn more, our minds open up.One could argue that whatever field one chooses, biology is so diverse that it is impossible to expose students to the entire bewildering array of biological phenomena; let us then at least try to understand the best-studied model systems and hope that they are in some sense representative examples of what goes on in nature. Fair point. But when it comes to sex at least, it is easy to become intrigued by its wonderful diversity. Why, then, do we still so narrow-mindedly stick to the familiar?In psychology, WEIRD is an a...

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Evolutionary mysteries in meiosis

Cited by 119 publications

References 191 publications

Genome Architecture and Evolution of a Unichromosomal Asexual Nematode

Genome Architecture and Evolution of a Unichromosomal Asexual Nematode

Cis-regulator runaway and divergence in asexuals

Weird sex: the underappreciated diversity of sexual reproduction

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