A genomic history of Aboriginal Australia.

The population history of Aboriginal Australians remains largely uncharacterized. Here we generate high-coverage genomes for 83 Aboriginal Australians (speakers of Pama-Nyungan languages) and 25 Papuans from the New Guinea Highlands. We find that Papuan and Aboriginal Australian ancestors diversified 25-40 thousand years ago (kya), suggesting pre-Holocene population structure in the ancient continent of Sahul (Australia, New Guinea and Tasmania). However, all of the studied Aboriginal Australians descend from a single founding population that differentiated ~10-32 kya. We infer a population expansion in northeast Australia during the Holocene epoch (past 10,000 years) associated with limited gene flow from this region to the rest of Australia, consistent with the spread of the Pama-Nyungan languages. We estimate that Aboriginal Australians and Papuans diverged from Eurasians 51-72 kya, following a single out-of-Africa dispersal, and subsequently admixed with archaic populations. Finally, we report evidence of selection in Aboriginal Australians potentially associated with living in the desert.

Deleterious protein-coding variants in diverse cattle breeds of the world.

The domestication of wild animals has resulted in a reduction in effective population sizes, which can affect the deleterious mutation load of domesticated breeds. In addition, artificial selection contributes to the accumulation of deleterious mutations because of an increased rate of inbreeding among domesticated animals. Since founder population sizes and artificial selection differ between cattle breeds, their deleterious mutation load can vary. We investigated this question by using whole-genome data from 432 animals belonging to 54 worldwide cattle breeds. Our analysis revealed a negative correlation between genomic heterozygosity and nonsynonymous-to-silent diversity ratio, which suggests a higher proportion of single nucleotide variants (SNVs) affecting proteins in low-diversity breeds. Our results also showed that low-diversity breeds had a larger number of high-frequency (derived allele frequency (DAF) > 0.51) deleterious SNVs than high-diversity breeds. An opposite trend was observed for the low-frequency (DAF ≤ 0.51) deleterious SNVs. Overall, the number of high-frequency deleterious SNVs was larger in the genomes of taurine cattle breeds than of indicine breeds, whereas the number of low-frequency deleterious SNVs was larger in the genomes of indicine cattle than in those of taurine cattle. Furthermore, we observed significant variation in the counts of deleterious SNVs within taurine breeds. The variations in deleterious mutation load between taurine and indicine breeds could be attributed to the population sizes of the wild progenitors before domestication, whereas the variations observed within taurine breeds could be due to differences in inbreeding level, strength of artificial selection, and/or founding population size. Our findings imply that the incidence of genetic diseases can vary between cattle breeds.

Abundance of clinical variants in exons included in multiple transcripts.

Previous studies showed that the magnitude of selection pressure in constitutive exons is higher than that in alternatively spliced exons. The intensity of selection was also shown to be depended on the inclusion level of exons: the number of transcripts that include an exon. Here, we examined how the difference in selection pressure influences the patterns of clinical variants in human exons. Our analysis revealed a positive relationship between exon inclusion level and the abundance of pathogenic variants. The proportion of pathogenic variants in the exons that are included in > 10 transcripts was 6.8 times higher than those in the exons included in only one transcript. This suggests that the mutations occurring in the exons included in multiple transcripts are more deleterious than those present in the exons included in one transcript. The findings of this study highlight that the exon inclusion level could be used to predict the mutations associated with diseases.

Population size influences the type of nucleotide variations in humans.

BACKGROUND: It is well known that the effective size of a population (Ne) is one of the major determinants of the amount of genetic variation within the population. However, it is unclear whether the types of genetic variations are also dictated by the effective population size. To examine this, we obtained whole genome data from over 100 populations of the world and investigated the patterns of mutational changes. RESULTS: Our results revealed that for low frequency variants, the ratio of AT→GC to GC→AT variants (ß) was similar across populations, suggesting the similarity of the pattern of mutation in various populations. However, for high frequency variants, ß showed a positive correlation with the effective population size of the populations. This suggests a much higher proportion of high frequency AT→GC variants in large populations (e.g. Africans) compared to those with small population sizes (e.g. Asians). These results imply that the substitution patterns vary significantly between populations. These findings could be explained by the effect of GC-biased gene conversion (gBGC), which favors the fixation of G/C over A/T variants in populations. In large population, gBGC causes high ß. However, in small populations, genetic drift reduces the effect of gBGC resulting in reduced ß. This was further confirmed by a positive relationship between Ne and ß for homozygous variants. CONCLUSIONS: Our results highlight the huge variation in the types of homozygous and high frequency polymorphisms between world populations. We observed the same pattern for deleterious variants, implying that the homozygous polymorphisms associated with recessive genetic diseases will be more enriched with G or C in populations with large Ne (e.g. Africans) than in populations with small Ne (e.g. Europeans).

A study on the efficacy of single layer full thickness duct to mucosa pancreatojejunostomy following pancreatoduodenectomy.

OBJECTIVE: Pancreatoduodenectomy is the procedure of choice for treating periampullary and pancreatic head malignancy. The procedure has been standardized and the mortality has reduced considerably to fewer than 5% in high volume centers specializing in pancreatic surgeries. Unfortunately, the morbidity still hovers around 40%. The Achiles heal of pancreatoduodenectomy is the pancreatoenteric anastamosis, the failure of which leads to significant morbidity. Literature is flooded with a plethora of techniques of reconstruction, and the results are variable. In this present study, we have analyzed a technique in which we used a single layer full thickness duct to mucosa pancreatojejunostomy. Among the 25 subjects in this study, there was only one case of one mortality due to drug-induced cardiac arrhythmia, and no mortality secondary to pancreas-specific complications were reported. The present study was a pilot study compared with historical controls, where these results were comparable to the historical data reported earlier as well as our own historical data of two-layered anastamosis. The results of this pilot study supported our concept of single layer full thickness duct to mucosa anastamosis being least traumatic to the pancreas and having an equal efficacy to that other conventional techniques.

Ancient mtDNA sequences from the First Australians revisited.

The publication in 2001 by Adcock et al. [Adcock GJ, et al. (2001) Proc Natl Acad Sci USA 98(2):537-542] in PNAS reported the recovery of short mtDNA sequences from ancient Australians, including the 42,000-y-old Mungo Man [Willandra Lakes Hominid (WLH3)]. This landmark study in human ancient DNA suggested that an early modern human mitochondrial lineage emerged in Asia and that the theory of modern human origins could no longer be considered solely through the lens of the "Out of Africa" model. To evaluate these claims, we used second generation DNA sequencing and capture methods as well as PCR-based and single-primer extension (SPEX) approaches to reexamine the same four Willandra Lakes and Kow Swamp 8 (KS8) remains studied in the work by Adcock et al. Two of the remains sampled contained no identifiable human DNA (WLH15 and WLH55), whereas the Mungo Man (WLH3) sample contained no Aboriginal Australian DNA. KS8 reveals human mitochondrial sequences that differ from the previously inferred sequence. Instead, we recover a total of five modern European contaminants from Mungo Man (WLH3). We show that the remaining sample (WLH4) contains ∼1.4% human DNA, from which we assembled two complete mitochondrial genomes. One of these was a previously unidentified Aboriginal Australian haplotype belonging to haplogroup S2 that we sequenced to a high coverage. The other was a contaminating modern European mitochondrial haplotype. Although none of the sequences that we recovered matched those reported by Adcock et al., except a contaminant, these findings show the feasibility of obtaining important information from ancient Aboriginal Australian remains.

Melioidosis-Series of Seven Cases from Madurai, Tamil Nadu, India.

We describe a case series of seven culture proven melioidosis patients presenting during 2014 to 2016 in Madurai, south Tamilnadu. Skin, soft tissue, bone and joint infections were common. All of them were middle aged men except one case. All the cases were reported during the monsoon season. Predisposing factors include diabetes and alcoholism. Despite many case reports and studies from South India, melioidosis still remains undiagnosed, hence under reported from many centers. Delayed diagnosis leads way to sepsis and other complications. Awareness about the preventive measures, earlier clinical and laboratory identification and appropriate management of severe sepsis are required to reduce the burden of this disease. HOW TO CITE THIS ARTICLE: Ganesan V, Sundaramoorthy R et al., Melioidosis-Series of Seven Cases from Madurai, Tamil Nadu, India. Indian J Crit Care Med 2019;23(3):149-151.

Effect of genetic drift on determinants of protein evolution.

A number of previous studies reported that gene expression, tissue specificity, gene essentiality and the number of protein-protein interactions influence the rate of protein evolution. Here we investigated the influence of effective population size (Ne) on these determinants of protein evolution. For this purpose, we compared the ratio of non-synonymous-to-synonymous diversities (πN/πS) estimated for protein-coding genes of Mus musculus castaneus and Mus musculus musculus: populations with high and low Ne respectively. Our results revealed that the difference between πN/πS estimated for genes with high and low expression levels was significantly smaller for M. m. musculus compared to that observed for M. m. castaneus The difference between the πN/πS of broadly expressed and tissue specific genes was much higher for M. m. castaneus compared to that of M. m. musculus. Furthermore, the difference between the πN/πS computed for essential and non-essential genes was much smaller for M. m. musculus than M. m. castaneus A similar pattern was observed for genes involved in many protein-protein interactions versus those involved in one. These results suggest that the effects of the determinants on protein evolution were much reduced for the population with small Ne due to increased genetic drift.

The effects of sample size on population genomic analyses--implications for the tests of neutrality.

BACKGROUND: One of the fundamental measures of molecular genetic variation is the Watterson's estimator (θ), which is based on the number of segregating sites. The estimation of θ is unbiased only under neutrality and constant population growth. It is well known that the estimation of θ is biased when these assumptions are violated. However, the effects of sample size in modulating the bias was not well appreciated. RESULTS: We examined this issue in detail based on large-scale exome data and robust simulations. Our investigation revealed that sample size appreciably influences θ estimation and this effect was much higher for constrained genomic regions than that of neutral regions. For instance, θ estimated for synonymous sites using 512 human exomes was 1.9 times higher than that obtained using 16 exomes. However, this difference was 2.5 times for the nonsynonymous sites of the same data. We observed a positive correlation between the rate of increase in θ estimates (with respect to the sample size) and the magnitude of selection pressure. For example, θ estimated for the nonsynonymous sites of highly constrained genes (dN/dS < 0.1) using 512 exomes was 3.6 times higher than that estimated using 16 exomes. In contrast this difference was only 2 times for the less constrained genes (dN/dS > 0.9). CONCLUSIONS: The results of this study reveal the extent of underestimation owing to small sample sizes and thus emphasize the importance of sample size in estimating a number of population genomic parameters. Our results have serious implications for neutrality tests such as Tajima D, Fu-Li D and those based on the McDonald and Kreitman test: Neutrality Index and the fraction of adaptive substitutions. For instance, use of 16 exomes produced 2.4 times higher proportion of adaptive substitutions compared to that obtained using 512 exomes (24% vs 10 %).

Europeans have a higher proportion of high­frequency deleterious variants than Africans.

Recent studies have shown that a high proportion of rare variants in European and African populations are deleterious in nature. However, the deleterious fraction of high-frequency variants is unclear. Using more than 6500 exomes we show a much higher fraction (11 %) of relatively high-frequency nonsynonymous (amino acid altering) variants (DAF 0.1­10 %) in European Americans (EA) compared to those from African Americans (AA). In contrast, this difference was only marginal (<2 %) for low-frequency nonsynonymous variants (DAF <0.1 %). Our results also revealed that the proportion of high-frequency deleterious nonsynonymous variants in EA was much higher (24 %) than that in AA and this difference was very small (4 %) for the low-frequency deleterious amino acid altering variants. We also show that EA have significantly more number of high-frequency deleterious nonsynonymous variants per genome than AA. The high proportion of high-frequency deleterious variants in EA could be the result of the well-known bottleneck experienced by European populations in which harmful mutations may have drifted to high frequencies. The estimated ages of deleterious variants support this prediction. Our results suggest that high-frequency variants could be relatively more likely to be associated with diseases in Europeans than in Africans and hence emphasize the need for population-specific strategies in genomic medicine studies.

Using the plurality of codon positions to identify deleterious variants in human exomes.

MOTIVATION: A codon position could perform different or multiple roles in alternative transcripts of a gene. For instance, a non-synonymous position in one transcript could be a synonymous site in another. Alternatively, a position could remain as non-synonymous in multiple transcripts. Here we examined the impact of codon position plurality on the frequency of deleterious single-nucleotide variations (SNVs) using data from 6500 human exomes. RESULTS: Our results showed that the proportion of deleterious SNVs was more than 2-fold higher in positions that remain non-synonymous in multiple transcripts compared with that observed in positions that are non-synonymous in one or some transcript(s) and synonymous or intronic in other(s). Furthermore, we observed a positive relationship between the fraction of deleterious non-synonymous SNVs and the number of proteins (alternative splice variants) affected. These results demonstrate that the plurality of codon positions is an important attribute, which could be useful in identifying mutations associated with diseases. CONTACT: s.subramanian@griffith.edu.au SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Genomic consequences of isolation and inbreeding in an island dingo population.

Dingoes come from an ancient canid lineage that originated in East Asia around 8000-11,000 years BP. As Australia's largest terrestrial predator, dingoes play an important ecological role. A small, protected population exists on a world heritage listed offshore island, K'gari (formerly Fraser Island). Concern regarding the persistence of dingoes on K'gari has risen due to their low genetic diversity and elevated inbreeding levels. However, whole-genome sequencing data is lacking from this population. Here, we include five new whole-genome sequences of K'gari dingoes. We analyze a total of 18 whole genome sequences of dingoes sampled from mainland Australia and K'gari to assess the genomic consequences of their demographic histories. Long (>1 Mb) runs of homozygosity (ROH) - indicators of inbreeding - are elevated in all sampled dingoes. However, K'gari dingoes showed significantly higher levels of very long ROH (>5 Mb), providing genomic evidence for small population size, isolation, inbreeding, and a strong founder effect. Our results suggest that, despite current levels of inbreeding, the K'gari population is purging strongly deleterious mutations, which, in the absence of further reductions in population size, may facilitate the persistence of small populations despite low genetic diversity and isolation. However, there may be little to no purging of mildly deleterious alleles, which may have important long-term consequences, and should be considered by conservation and management programs.

Genomic Consequences of Isolation and Inbreeding in an Island Dingo Population.

Dingoes come from an ancient canid lineage that originated in East Asia around 8,000 to 11,000 years BP. As Australia's largest terrestrial predator, dingoes play an important ecological role. A small, protected population exists on a world heritage listed offshore island, K'gari (formerly Fraser Island). Concern regarding the persistence of dingoes on K'gari has risen due to their low genetic diversity and elevated inbreeding levels. However, whole-genome sequence data is lacking from this population. Here, we include five new whole-genome sequences of K'gari dingoes. We analyze a total of 18 whole-genome sequences of dingoes sampled from mainland Australia and K'gari to assess the genomic consequences of their demographic histories. Long (>1 Mb) runs of homozygosity (ROHs)-indicators of inbreeding-are elevated in all sampled dingoes. However, K'gari dingoes showed significantly higher levels of very long ROH (>5 Mb), providing genomic evidence for small population size, isolation, inbreeding, and a strong founder effect. Our results suggest that, despite current levels of inbreeding, the K'gari population is purging strongly deleterious mutations, which, in the absence of further reductions in population size, may facilitate the persistence of small populations despite low genetic diversity and isolation. However, there may be little to no purging of mildly deleterious alleles, which may have important long-term consequences, and should be considered by conservation and management programs.

Evidence for a recent origin of penguins.

Penguins are a remarkable group of birds, with the 18 extant species living in diverse climatic zones from the tropics to Antarctica. The timing of the origin of these extant penguins remains controversial. Previous studies based on DNA sequences and fossil records have suggested widely differing times for the origin of the group. This has given rise to widely differing biogeographic narratives about their evolution. To resolve this problem, we sequenced five introns from 11 species representing all genera of living penguins. Using these data and other available DNA sequences, together with the ages of multiple penguin fossils to calibrate the molecular clock, we estimated the age of the most recent common ancestor of extant penguins to be 20.4 Myr (17.0-23.8 Myr). This time is half of the previous estimates based on molecular sequence data. Our results suggest that most of the major groups of extant penguins diverged 11-16 Ma. This overlaps with the sharp decline in Antarctic temperatures that began approximately 12 Ma, suggesting a possible relationship between climate change and penguin evolution.

Genomic footprints of bottleneck in landlocked salmon population.

At the end of the last ice age, several Atlantic salmon populations got caught up in the lakes and ponds of the Northern Hemisphere. Occasionally, the populations also got locked when the flow of rivers terminated from reaching the sea due to land upheaval. Therefore, the pattern of evolution shaping the landlocked salmon populations is different from the other anadromous salmons, which migrate between the sea and rivers. According to the theories of population genetics, the effect of genetic drift is expected to be more pronounced in the former compared to the latter. Here we examined this using the whole genome data of landlocked and anadromous salmon populations of Norway. Our results showed a 50-80% reduction in the genomic heterozygosity in the landlocked compared to anadromous salmon populations. The number and total size of the runs of homozygosity (RoH) segments of landlocked salmons were two to eightfold higher than those of their anadromous counterparts. We found the former had a higher ratio of nonsynonymous-to-synonymous diversities than the latter. The investigation also revealed a significant elevation of homozygous deleterious Single Nucleotide Variants (SNVs) in the landlocked salmon compared to the anadromous populations. All these results point to a significant reduction in the population size of the landlocked salmons. This process of reduction might have started recently as the phylogeny revealed a recent separation of the landlocked from the anadromous population. Previous studies on terrestrial vertebrates observed similar signatures of a bottleneck when the populations from Island and the mainland were compared. Since landlocked waterbody such as ponds and lakes are geographically analogous to Islands for fish populations, the findings of this study suggest the similarity in the patterns of evolution between the two.

Genomic signatures of bottleneck and founder effects in dingoes.

Dingoes arrived in Australia during the mid-Holocene and are the top-order terrestrial predator on the continent. Although dingoes subsequently spread across the continent, the initial founding population(s) could have been small. We investigated this hypothesis by sequencing the whole genomes of three dingoes and also obtaining the genome data from nine additional dingoes and 56 canines, including wolves, village dogs and breed dogs, and examined the signatures of bottlenecks and founder effects. We found that the nucleotide diversity of dingoes was low, 36% less than highly inbred breed dogs and 3.3 times lower than wolves. The number of runs of homozygosity (RoH) segments in dingoes was 1.6-4.7 times higher than in other canines. While examining deleterious mutational load, we observed that dingoes carried elevated ratios of nonsynonymous-to-synonymous diversities, significantly higher numbers of homozygous deleterious Single Nucleotide Variants (SNVs), and increased numbers of loss of function SNVs, compared to breed dogs, village dogs, and wolves. Our findings can be explained by bottlenecks and founder effects during the establishment of dingoes in mainland Australia. These findings highlight the need for conservation-based management of dingoes and the need for wildlife managers to be cognisant of these findings when considering the use of lethal control measures across the landscape.

High proportions of deleterious polymorphisms in constrained human genes.

Previous studies on human mitochondrial genomes showed that the ratio of intra-specific diversities at nonsynonymous-to-synonymous positions was two to ten times higher than the ratio of interspecific divergences at these positions, suggesting an excess of slightly deleterious nonsynonymous polymorphisms. However, such an overabundance of nonsynonymous single nucleotide polymorphisms (SNPs) was not found in human nuclear genomes. Here, genome-wide estimates using >14,000 human-chimp nuclear genes and 1 million SNPs from four human genomes showed a significant proportion of deleterious nonsynonymous SNPs (∼ 15%). Importantly, this study reveals a negative correlation between the magnitude of selection pressure and the proportion of deleterious SNPs on human genes. The proportion of deleterious amino acid replacement polymorphisms is 3.5 times higher in genes under high purifying selection compared with that in less constrained genes (28% vs. 8%). These results are explained by differences in the extent of contribution of mildly deleterious mutations to diversity and substitution.

Fixation of deleterious mutations at critical positions in human proteins.

Deleterious mutations associated with human diseases are predominantly found in conserved positions and positions that are essential for the structure and/or function of proteins. However, these mutations are purged from the human population over time and prevented from being fixed. Contrary to this belief, here I show that high proportions of deleterious amino acid changing mutations are fixed at positions critical for the structure and/or function of proteins. Similarly, a high rate of fixation of deleterious mutations was observed in slow-evolving amino acid positions of human proteins. The fraction of deleterious substitutions was found to be two times higher in relatively conserved amino acid positions than in highly variable positions. This study also found fixation of a much higher proportion of radical amino acid changes in primates compared with rodents and artiodactyls in slow-evolving positions. Previous studies observed a higher proportion of nonsynonymous substitutions in humans compared with other mammals, which was taken as indirect evidence for the fixation of deleterious mutations in humans. However, the results of this investigation provide direct evidence for this prediction by suggesting that the excess nonsynonymous mutations fixed in humans are indeed deleterious in nature. Furthermore, these results suggest that studies on disease-associated mutations should consider that a significant fraction of such deleterious mutations has already been fixed in the human genome, and thus, the effects of new mutations at those amino acid positions may not necessarily be deleterious and might even result in reversion to benign phenotypes.

High mitogenomic evolutionary rates and time dependency.

Using entire modern and ancient mitochondrial genomes of Adélie penguins (Pygoscelis adeliae) that are up to 44000 years old, we show that the rates of evolution of the mitochondrial genome are two to six times greater than those estimated from phylogenetic comparisons. Although the rate of evolution at constrained sites, including nonsynonymous positions and RNAs, varies more than twofold with time (between shallow and deep nodes), the rate of evolution at synonymous sites remains the same. The time-independent neutral evolutionary rates reported here would be useful for the study of recent evolutionary events.

The Difference in the Proportions of Deleterious Variations within and between Populations Influences the Estimation of FST.

Estimating the extent of genetic differentiation between populations is an important measure in population genetics, ecology and evolutionary biology. The fixation index, or FST, is an important measure, which is routinely used to quantify this. Previous studies have shown that the FST estimated for selectively constrained regions was significantly lower than that estimated for neutral regions. By deriving the theoretical relationship between FST at neutral and constrained sites, we show that excess in the fraction of deleterious variations segregating within populations compared to those segregating between populations is the cause for the reduction in FST estimated at constrained sites. Using whole-genome data, our results revealed that the magnitude of reduction in FST estimates obtained for selectively constrained regions was much higher for distantly related populations compared to those estimated for closely related pairs. For example, the reduction was 47% for comparison between Europeans and Africans, 30% for the European and Asian comparison, 16% for the Northern and Southern European pair, and only 4% for the comparison involving two Southern European (Italian and Spanish) populations. Since deleterious variants are purged over time due to purifying selection, their contribution to the among-population diversity at constrained sites decreases with the increase in the divergence between populations. However, within-population diversities remain the same for all pairs compared; therefore, the FST estimated at constrained sites for distantly related populations are much smaller than those estimated for closely related populations. We obtained similar results when only the SNPs with similar allele frequencies at neutral and constrained sites were used. Our results suggest that the level of population divergence should be considered when comparing constrained site FST estimates from different pairs of populations.