Project description:Here we reassess available evidence for the long-held misconception of amoebae possessing exceptionally large genomes. Traditionally, estimates relied on inaccurate methods like DNA weight measurements, leading to inflated sizes. These methods failed to account for contaminating DNA from prey, endosymbionts, and intrinsic genomic features like ribosomal operon amplification. Modern sequencing techniques unveil a different picture. Fully sequenced amoebozoa genomes range from 14.4 to 52.37 mega basepairs, well within the typical single-celled eukaryote expectation. While the whole genome of the historically relevant Amoeba proteus has not yet been fully sequenced, we provide here a statistical analysis using protein-coding genes from transcriptomic data, suggesting that the genome size is consistent with this range, far smaller than previously claimed. The misconception likely originated in the early 21st century and perpetuated through popular science materials. We conclude that there is no longer reason to reaffirm that amoeba genomes are giant.

| S-EPMC11773323 | biostudies-literature

Mutation rate variation at human dinucleotide microsatellites.

Project description:Mutation is the ultimate source of genetic variation, and mutation rate is thus an important parameter governing the extent of genetic variation. Microsatellites are highly informative genetic markers that have been widely used in genetic studies. While previous studies showed that the mutation rate differs in di-, tri-, and tetranucleotide repeats, how mutation rate distributes within each class of repeat is poorly understood. This study first revealed the pattern of the mutation rate variation within the dinucleotide repeats. Two data sets were used. The first is the allele frequency data from 115 microsatellites with dinucleotide repeats distributed along the human genome in 10 worldwide populations. The second data set is much larger, consisting of the allele frequency of 5252 dinucleotide repeats from the Genome Database. Mutation rate for each locus is estimated through a new homozygosity-based estimator, which has been shown to be unbiased and highly efficient and is reasonably robust against deviations from the single-step model. The mutation rates among loci can be approximated well by a gamma distribution and its shape parameter can be accurately estimated with this approach. This result provides the basic guidelines for analyzing the large-scale genomic data from microsatellite loci.

| S-EPMC1449715 | biostudies-literature

Cryptic variation in the human mutation rate.

Project description:The mutation rate is known to vary between adjacent sites within the human genome as a consequence of context, the most well-studied example being the influence of CpG dinucelotides. We investigated whether there is additional variation by testing whether there is an excess of sites at which both humans and chimpanzees have a single-nucleotide polymorphism (SNP). We found a highly significant excess of such sites, and we demonstrated that this excess is not due to neighbouring nucleotide effects, ancestral polymorphism, or natural selection. We therefore infer that there is cryptic variation in the mutation rate. However, although this variation in the mutation rate is not associated with the adjacent nucleotides, we show that there are highly nonrandom patterns of nucleotides that extend approximately 80 base pairs on either side of sites with coincident SNPs, suggesting that there are extensive and complex context effects. Finally, we estimate the level of variation needed to produce the excess of coincident SNPs and show that there is a similar, or higher, level of variation in the mutation rate associated with this cryptic process than there is associated with adjacent nucleotides, including the CpG effect. We conclude that there is substantial variation in the mutation that has, until now, been hidden from view.

| S-EPMC2634788 | biostudies-literature

Phenotype switching of the mutation rate facilitates adaptive evolution.

Project description:The mutation rate plays an important role in adaptive evolution. It can be modified by mutator and anti-mutator alleles. Recent empirical evidence hints that the mutation rate may vary among genetically identical individuals: evidence from bacteria suggests that the mutation rate can be affected by expression noise of a DNA repair protein and potentially also by translation errors in various proteins. Importantly, this non-genetic variation may be heritable via a transgenerational epigenetic mode of inheritance, giving rise to a mutator phenotype that is independent from mutator alleles. Here, we investigate mathematically how the rate of adaptive evolution is affected by the rate of mutation rate phenotype switching. We model an asexual population with two mutation rate phenotypes, non-mutator and mutator. An offspring may switch from its parental phenotype to the other phenotype. We find that switching rates that correspond to so-far empirically described non-genetic systems of inheritance of the mutation rate lead to higher rates of adaptation on both artificial and natural fitness landscapes. These switching rates can maintain within the same individuals both a mutator phenotype and intermediary mutations, a combination that facilitates adaptation. Moreover, non-genetic inheritance increases the proportion of mutators in the population, which in turn increases the probability of hitchhiking of the mutator phenotype with adaptive mutations. This in turns facilitates the acquisition of additional adaptive mutations. Our results rationalize recently observed noise in the expression of proteins that affect the mutation rate and suggest that non-genetic inheritance of this phenotype may facilitate evolutionary adaptive processes.

| S-EPMC10471227 | biostudies-literature

Re-evaluating the morphological evidence for the re-evolution of lost mandibular teeth in frogs.

Project description:Dollo's law of irreversibility states that once a complex structure is lost, it cannot be regained in the same form. Several putative exceptions to Dollo's law have been identified using phylogenetic comparative methods, but the anatomy and development of these traits are often poorly understood. Gastrotheca guentheri is renowned as the only frog with teeth on the lower jaw. Mandibular teeth were lost in the ancestor of frogs more than 200 million years ago and subsequently regained in G. guentheri. Little is known about the teeth in this species despite being a frequent example of trait "re-evolution," leaving open the possibility that it may have mandibular pseudoteeth. We assessed the dental anatomy of G. guentheri using micro-computed tomography and histology and confirmed the longstanding assumption that true mandibular teeth are present. Remarkably, the mandibular teeth of G. guentheri are nearly identical in gross morphology and development to upper jaw teeth in closely related species. The developmental genetics of tooth formation are unknown in this possibly extinct species. Our results suggest that an ancestral odontogenic pathway has been conserved but suppressed in the lower jaw since the origin of frogs, providing a possible mechanism underlying the re-evolution of lost mandibular teeth.

| S-EPMC9299036 | biostudies-literature

Mutation rate variability as a driving force in adaptive evolution.

Project description:Mutation rate is a key determinant of the pace as well as outcome of evolution, and variability in this rate has been shown in different scenarios to play a key role in evolutionary adaptation and resistance evolution under stress caused by selective pressure. Here we investigate the dynamics of resistance fixation in a bacterial population with variable mutation rates, and we show that evolutionary outcomes are most sensitive to mutation rate variations when the population is subject to environmental and demographic conditions that suppress the evolutionary advantage of high-fitness subpopulations. By directly mapping a biophysical fitness function to the system-level dynamics of the population, we show that both low and very high, but not intermediate, levels of stress in the form of an antibiotic result in a disproportionate effect of hypermutation on resistance fixation. We demonstrate how this behavior is directly tied to the extent of genetic hitchhiking in the system, the propagation of high-mutation rate cells through association with high-fitness mutations. Our results indicate a substantial role for mutation rate flexibility in the evolution of antibiotic resistance under conditions that present a weak advantage over wildtype to resistant cells.

| S-EPMC6819004 | biostudies-literature

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