scholarly journals A test of the hypothesis that variable mutation rates create signals that have previously been interpreted as evidence of archaic introgression into humans

2020 ◽  
Author(s):  
William Amos
Keyword(s):  
Mutation Rate ◽  
Alternative Model ◽  
Mutation Rates ◽  
Human Populations ◽  
Common Cause ◽  
Coalescent Simulations ◽  
Recurrent Mutations ◽  
Archaic Introgression ◽  
Excess Base ◽  
Human Specific

AbstractIt is widely accepted that non-African humans carry 1-2% Neanderthal DNA due to historical inter-breeding. However, inferences about introgression rely on a critical assumption that mutation rate is constant and that back-mutations are too rare to be important. Both these assumptions have been challenged, and recent evidence points towards an alternative model where signals interpreted as introgression are driven mainly by higher mutation rates in Africa. In this model, non-Africans appear closer to archaics not because they harbour introgressed fragments but because Africans have diverged more. Here I test this idea by using the density of rare, human-specific variants (RHSVs) as a proxy for recent mutation rate. I find that sites that contribute most to the signal interpreted as introgression tend to occur in tightly defined regions spanning only a few hundred bases in which mutation rate differs greatly between the two human populations being compared. Mutation rate is invariably higher in the population into which introgression is not inferred. I confirmed that RHSV density reflects mutation rate by conducting a parallel analysis looking at the density of RHSVs around sites with three alleles, an independent class of site that also requires recurrent mutations to form. Near-identical peaks in RHSV density are found, suggesting a common cause. Similarly, coalescent simulations confirm that, with constant mutation rate, introgressed fragments do not occur preferentially in regions with a high density of rare, human-specific variants. Together, these observations are difficult to reconcile with a model where excess base-sharing is driven by archaic legacies but instead provide support for a higher mutation rate inside Africa driving increased divergence from the ancestral human state.

scholarly journals Decomposing the admixture statistic, D, suggests a negligible contribution due to archaic introgression into humans

2021 ◽  
Author(s):  
William Amos
Keyword(s):  
Mutation Rate ◽  
Alternative Model ◽  
Human Populations ◽  
Ancestral State ◽  
Cpg Motifs ◽  
Archaic Introgression ◽  
Negligible Contribution

AbstractIt is widely accepted that non-African humans carry a few percent of Neanderthal DNA due to historical inter-breeding. However, methods used to infer a legacy all assume that mutation rate is constant and that back-mutations can be ignored. Here I decompose the widely used admixture statistic, D, in a way that allows the overall signal to be apportioned to different classes of contributing site. I explore three main characteristics: whether the putative Neanderthal allele is likely derived or ancestral; whether an allele is fixed in one of the two human populations; and the type of mutation that created the polymorphism, defined by the base that mutated and immediately flanking bases. The entire signal used to infer introgression can be attributed to a subset of sites where the putative Neanderthal base is common in Africans and fixed in non-Africans. Moreover, the four triplets containing highly mutable CpG motifs alone contribute 29%. In contrast, sites expected to dominate the signal if introgression has occurred, where the putative Neanderthal allele is absent from Africa and rare outside Africa, contribute negligibly. Together, these observations show that D does not capture a signal due to introgression but instead they support an alternative model in which a higher mutation rate in Africa drives increased divergence from the ancestral state.

scholarly journals Transfer RNA genes experience exceptionally elevated mutation rates

2018 ◽  
Vol 115 (36) ◽  
pp. 8996-9001 ◽  
Author(s):  
Bryan P. Thornlow ◽  
Josh Hough ◽  
Jacquelyn M. Roger ◽  
Henry Gong ◽  
Todd M. Lowe ◽  
...  
Keyword(s):  
Mutation Rate ◽  
Trna Gene ◽  
Gene Evolution ◽  
Purifying Selection ◽  
Mutation Rates ◽  
Model Organisms ◽  
Biological Synthesis ◽  
Human Populations ◽  
Trna Genes ◽  
Simple Method

Transfer RNAs (tRNAs) are a central component for the biological synthesis of proteins, and they are among the most highly conserved and frequently transcribed genes in all living things. Despite their clear significance for fundamental cellular processes, the forces governing tRNA evolution are poorly understood. We present evidence that transcription-associated mutagenesis and strong purifying selection are key determinants of patterns of sequence variation within and surrounding tRNA genes in humans and diverse model organisms. Remarkably, the mutation rate at broadly expressed cytosolic tRNA loci is likely between 7 and 10 times greater than the nuclear genome average. Furthermore, evolutionary analyses provide strong evidence that tRNA genes, but not their flanking sequences, experience strong purifying selection acting against this elevated mutation rate. We also find a strong correlation between tRNA expression levels and the mutation rates in their immediate flanking regions, suggesting a simple method for estimating individual tRNA gene activity. Collectively, this study illuminates the extreme competing forces in tRNA gene evolution and indicates that mutations at tRNA loci contribute disproportionately to mutational load and have unexplored fitness consequences in human populations.

scholarly journals Appropriate Assignment of Fossil Calibration Information Minimizes the Difference between Phylogenetic and Pedigree Mutation Rates in Humans

Life ◽  
2018 ◽  
Vol 8 (4) ◽  
pp. 49 ◽  
Author(s):  
Renata Capellão ◽  
Elisa Costa-Paiva ◽  
Carlos Schrago
Keyword(s):  
Mutation Rate ◽  
Divergence Time ◽  
Mutation Rates ◽  
Human Populations ◽  
Fossil Calibration ◽  
Divergence Time Estimates ◽  
Time Estimates ◽  
The Mean ◽  
The Difference ◽  
Coalescent Time

Studies that measured mutation rates in human populations using pedigrees have reported values that differ significantly from rates estimated from the phylogenetic comparison of humans and chimpanzees. Consequently, exchanges between mutation rate values across different timescales lead to conflicting divergence time estimates. It has been argued that this variation of mutation rate estimates across hominoid evolution is in part caused by incorrect assignment of calibration information to the mean coalescent time among loci, instead of the true genetic isolation (speciation) time between humans and chimpanzees. In this study, we investigated the feasibility of estimating the human pedigree mutation rate using phylogenetic data from the genomes of great apes. We found that, when calibration information was correctly assigned to the human–chimpanzee speciation time (and not to the coalescent time), estimates of phylogenetic mutation rates were statistically equivalent to the estimates previously reported using studies of human pedigrees. We conclude that, within the range of biologically realistic ancestral generation times, part of the difference between whole-genome phylogenetic and pedigree mutation rates is due to inappropriate assignment of fossil calibration information to the mean coalescent time instead of the speciation time. Although our results focus on the human–chimpanzee divergence, our findings are general, and relevant to the inference of the timescale of the tree of life.

scholarly journals Transfer RNA genes experience exceptionally elevated mutation rates

2017 ◽  
Author(s):  
Bryan P. Thornlow ◽  
Josh Hough ◽  
Jacquelyn M. Roger ◽  
Henry Gong ◽  
Todd M. Lowe ◽  
...  
Keyword(s):  
Mutation Rate ◽  
Sequence Variation ◽  
Trna Gene ◽  
Purifying Selection ◽  
Transfer Rna ◽  
Mutation Rates ◽  
Biological Synthesis ◽  
Human Populations ◽  
Trna Genes ◽  
Mutational Load

AbstractTransfer RNAs (tRNAs) are a central component for the biological synthesis of proteins, and they are among the most highly conserved and frequently transcribed genes in all living things. Despite their clear significance for fundamental cellular processes, the forces governing tRNA evolution are poorly understood. We present evidence that transcription-associated mutagenesis and strong purifying selection are key determinants of patterns of sequence variation within and surrounding tRNA genes in humans and diverse model organisms. Remarkably, the mutation rate at broadly expressed cytosolic tRNA loci is likely between seven and ten times greater than the nuclear genome average. Furthermore, evolutionary analyses provide strong evidence that tRNA genes, but not their flanking sequences, experience strong purifying selection, acting against this elevated mutation rate. We also find a strong correlation between tRNA expression levels and the mutation rates in their immediate flanking regions, suggesting a simple new method for estimating individual tRNA gene activity. Collectively, this study illuminates the extreme competing forces in tRNA gene evolution, and implies that mutations at tRNA loci contribute disproportionately to mutational load and have unexplored fitness consequences in human populations.Significance StatementWhile transcription-associated mutagenesis (TAM) has been demonstrated for protein coding genes, its implications in shaping genome structure at transfer RNA (tRNA) loci in metazoans have not been fully appreciated. We show that cytosolic tRNAs are a striking example of TAM because of their variable rates of transcription, well-defined boundaries and internal promoter sequences. tRNA loci have a mutation rate approximately seven-to tenfold greater than the genome-wide average, and these mutations are consistent with signatures of TAM. These observations indicate that tRNA loci are disproportionately large contributors to mutational load in the human genome. Furthermore, the correlations between tRNA locus variation and transcription implicate that prediction of tRNA gene expression based on sequence variation data is possible.

scholarly journals Sequence dependencies and mutation rates of localized mutational processes in cancer

2021 ◽  
Author(s):  
Gustav Alexander Poulsgaard ◽  
Simon Grund Sørensen ◽  
Randi Istrup Juul ◽  
Morten Muhlig Nielsen ◽  
Jakob Skou Pedersen
Keyword(s):  
Mutation Rate ◽  
Genomic Sequence ◽  
Mutation Rates ◽  
Unknown Etiology ◽  
Mutational Signatures ◽  
Data Set ◽  
Recurrent Mutations ◽  
Mutational Hotspots ◽  
Pan Cancer ◽  
Mutational Processes

Background: Cancer mutations accumulate through replication errors and DNA damage coupled with incomplete repair. Individual mutational processes often show strong sequence and regional preferences. As a result, some sequence contexts mutate at much higher rates than others. Mutational hotspots, with recurrent mutations across cancer samples, represent genomic positions with elevated mutation rates, often caused by highly localized mutational processes. Results: We analyze the mutation rates of all 11-mer genomic sequence contexts using the PCAWG set of 2,583 pan-cancer whole genomes. We further associate individual mutations and contexts to mutational signatures and estimate their relative mutation rates. We show that hotspots generally identify highly mutable sequence contexts. Using these, we show that some mutational signatures are enriched in hotspot sequence contexts, corresponding to well-defined sequence preferences for the underlying localized mutational processes. This includes signature 17b (of unknown etiology) and signatures 62 (POLE), 7a (UV), and 72 (linked to lymphomas). In some cases, the mutation rate increases further when focusing on certain genomic regions, such as signature 62 in poised promoters, where the mutation is increased several thousand folds over the overall data set average. Conclusion: We summarize our findings in a catalog of localized mutational processes, their sequence preferences, and their estimated mutation rates. Keywords: pan-cancer, mutational processes, hotspots, mutation rate

scholarly journals Mutation rate analysis via parent–progeny sequencing of the perennial peach. II. No evidence for recombination-associated mutation

2016 ◽  
Vol 283 (1841) ◽  
pp. 20161785 ◽  
Author(s):  
Long Wang ◽  
Yanchun Zhang ◽  
Chao Qin ◽  
Dacheng Tian ◽  
Sihai Yang ◽  
...  
Keyword(s):  
Mutation Rate ◽  
Recombination Rate ◽  
Mutation Rates ◽  
Recombination Rates ◽  
Rate Analysis ◽  
A Genome ◽  
Break Points ◽  
New Mutations

Mutation rates and recombination rates vary between species and between regions within a genome. What are the determinants of these forms of variation? Prior evidence has suggested that the recombination might be mutagenic with an excess of new mutations in the vicinity of recombination break points. As it is conjectured that domesticated taxa have higher recombination rates than wild ones, we expect domesticated taxa to have raised mutation rates. Here, we use parent–offspring sequencing in domesticated and wild peach to ask (i) whether recombination is mutagenic, and (ii) whether domesticated peach has a higher recombination rate than wild peach. We find no evidence that domesticated peach has an increased recombination rate, nor an increased mutation rate near recombination events. If recombination is mutagenic in this taxa, the effect is too weak to be detected by our analysis. While an absence of recombination-associated mutation might explain an absence of a recombination–heterozygozity correlation in peach, we caution against such an interpretation.

Evolution of mutation rate and virulence among human retroviruses

1994 ◽  
Vol 346 (1317) ◽  
pp. 333-343 ◽  
Keyword(s):  
Immune System ◽  
Mutation Rate ◽  
Hiv Infections ◽  
Molecular Data ◽  
Mutation Rates ◽  
Rapid Progression ◽  
Human T Cell ◽  
Large Numbers ◽  
The Individual ◽  
Multicellular Organisms

High mutation rates are generally considered to be detrimental to the fitness of multicellular organisms because mutations untune finely tuned biological machinery. However, high mutation rates may be favoured by a need to evade an immune system that has been strongly stimulated to recognize those variants that reproduced earlier during the infection, hiv infections conform to this situation because they are characterized by large numbers of viruses that are continually breaking latency and large numbers that are actively replicating throughout a long period of infection. To be transmitted, HIVS are thus generally exposed to an immune system that has been activated to destroy them in response to prior viral replication in the individual. Increases in sexual contact should contribute to this predicament by favouring evolution toward relatively high rates of replication early during infection. Because rapid replication and high mutation rate probably contribute to rapid progression of infections to aids, the interplay of sexual activity, replication rate, and mutation rate helps explain why HIV-1 has only recently caused a lethal pandemic, even though molecular data suggest that it may have been present in humans for more than a century. This interplay also offers an explanation for geographic differences in progression to cancer found among infections due to the other major group of human retroviruses, human T-cell lymphotropic viruses (HTLV). Finally, it suggests ways in which we can use natural selection as a tool to control the aids pandemic and prevent similar pandemics from arising in the future.

Y-chromosomal microsatellite mutation rates: Differences in mutation rate between and within loci

2004 ◽  
Vol 23 (2) ◽  
pp. 117-124 ◽  
Author(s):  
B. Myhre Dupuy ◽  
M. Stenersen ◽  
T. Egeland ◽  
B. Olaisen
Keyword(s):  
Mutation Rate ◽  
Mutation Rates ◽  
Microsatellite Mutation

scholarly journals Novel start codons introduce novel coding sequences in the human genomes

2020 ◽  
Author(s):  
He Zhang ◽  
Yang Xie
Keyword(s):  
Translation Initiation ◽  
Genomic Analysis ◽  
Comparative Genomic ◽  
Human Populations ◽  
The Novel ◽  
Coding Sequences ◽  
Human Genomes ◽  
High Level ◽  
Selection Signal ◽  
Human Specific

AbstractStart-gain mutations can introduce novel start codons and generate novel coding sequences that may affect the function of genes. In this study, we systematically investigated the novel start codons that were either polymorphic or fixed in the human genomes. 829 polymorphic start-gain SNVs were identified in the human populations, and the novel start codons introduced by these SNVs have significantly higher activity in translation initiation. Some of these start-gain SNVs were reported to be associated with phenotypes and diseases in previous studies. By comparative genomic analysis, we found 26 human-specific start codons that were fixed after the divergence between the human and chimpanzee, and high-level translation initiation activity was observed on them. The negative selection signal was detected in the novel coding sequences introduced by these human-specific start codons, indicating the important function of these novel coding sequences. This study reveals start-gain mutations are keeping appearing in the human genomes during the evolution and may be important sources altering the function of genes which may further affect the phenotypes or cause diseases.

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