| 1. |
|
|
| 2. |
- Axelsson, Erik, et al.
(författare)
-
Comparison of the chicken and turkey genomes reveals a higher rate of nucleotide divergence on microchromosomes than macrochromosomes.
- 2005
-
Ingår i: Genome Res. - 1088-9051. ; 15:1, s. 120-5
-
Tidskriftsartikel (refereegranskat)abstract
- A distinctive feature of the avian genome is the large heterogeneity in the size of chromosomes, which are usually classified into a small number of macrochromosomes and numerous microchromosomes. These chromosome classes show characteristic differences in a number of interrelated features that could potentially affect the rate of sequence evolution, such as GC content, gene density, and recombination rate. We studied the effects of these factors by analyzing patterns of nucleotide substitution in two sets of chicken-turkey sequence alignments. First, in a set of 67 orthologous introns, divergence was significantly higher in microchromosomes (chromosomes 11-38; 11.7% divergence) than in both macrochromosomes (chromosomes 1-5; 9.9% divergence; P = 0.016) and intermediate-sized chromosomes (chromosomes 6-10; 9.5% divergence; P = 0.026). At least part of this difference was due to the higher incidence of CpG sites on microchromosomes. Second, using 155 orthologous coding sequences we noted a similar pattern, in which synonymous substitution rates on microchromosomes (13.1%) were significantly higher than were rates on macrochromosomes (10.3%; P = 0.024). Broadly assuming neutrality of introns and synonymous sites, or constraints on such sequences do not differ between chromosomal classes, these observations imply that microchromosomal genes are exposed to more germ line mutations than those on other chromosomes. We also find that dN/dS ratios for genes located on microchromosomes (average, 0.094) are significantly lower than those of macrochromosomes (average, 0.185; P = 0.025), suggesting that the proteins of genes on microchromosomes are under greater evolutionary constraint.
|
|
| 3. |
- Belle, Elise M S, et al.
(författare)
-
Why are young and old repetitive elements distributed differently in the human genome?
- 2005
-
Ingår i: J Mol Evol. - 0022-2844. ; 60:3, s. 290-6
-
Tidskriftsartikel (refereegranskat)abstract
- Alu elements are not distributed homogeneously throughout the human genome: old elements are preferentially found in the GC-rich parts of the genome, while young Alus are more often found in the GC-poor parts of the genome. The process giving rise to this differential distribution remains poorly understood. Here we investigate whether this pattern could be due to a preferential degradation of Alu elements integrated in GC-poor regions by small indel mutations. We aligned 5.1 Mb of human and chimpanzee sequences and examined whether the rate of insertion and deletion inside Alu elements differed according to the base composition surrounding them. We found that Alu elements are not preferentially degraded in GC-poor regions by indel events. We also looked at whether very young L1 elements show the same change in distribution compared to older ones. This analysis indicated that L1 elements also show a shift in their distribution, although we could not assess it as precisely as for Alu elements. We propose that the differential distribution of Alu elements is likely to be due to a change in their pattern of insertion or their probability of fixation through evolutionary time.
|
|
| 4. |
- Berglund, Jonas, et al.
(författare)
-
Hotspots of biased nucleotide substitutions in human genes
- 2009
-
Ingår i: PLoS biology. - : Public Library of Science (PLoS). - 1544-9173 .- 1545-7885. ; 7:1, s. e26-
-
Tidskriftsartikel (refereegranskat)abstract
- Genes that have experienced accelerated evolutionary rates on the human lineage during recent evolution are candidates for involvement in human-specific adaptations. To determine the forces that cause increased evolutionary rates in certain genes, we analyzed alignments of 10,238 human genes to their orthologues in chimpanzee and macaque. Using a likelihood ratio test, we identified protein-coding sequences with an accelerated rate of base substitutions along the human lineage. Exons evolving at a fast rate in humans have a significant tendency to contain clusters of AT-to-GC (weak-to-strong) biased substitutions. This pattern is also observed in noncoding sequence flanking rapidly evolving exons. Accelerated exons occur in regions with elevated male recombination rates and exhibit an excess of nonsynonymous substitutions relative to the genomic average. We next analyzed genes with significantly elevated ratios of nonsynonymous to synonymous rates of base substitution (dN/dS) along the human lineage, and those with an excess of amino acid replacement substitutions relative to human polymorphism. These genes also show evidence of clusters of weak-to-strong biased substitutions. These findings indicate that a recombination-associated process, such as biased gene conversion (BGC), is driving fixation of GC alleles in the human genome. This process can lead to accelerated evolution in coding sequences and excess amino acid replacement substitutions, thereby generating significant results for tests of positive selection.
|
|
| 5. |
- Björnerfeldt, Susanne, et al.
(författare)
-
Relaxation of selective constraint on dog mitochondrial DNA following domestication
- 2006
-
Ingår i: Genome Research. - : Cold Spring Harbor Laboratory. - 1088-9051 .- 1549-5469. ; 16:8, s. 990-994
-
Tidskriftsartikel (refereegranskat)abstract
- The domestication of dogs caused a dramatic change in their way of life compared with that of their ancestor, the gray wolf. We hypothesize that this new life style changed the selective forces that acted upon the species, which in turn had an effect on the dog's genome. We sequenced the complete mitochondrial DNA genome in 14 dogs, six wolves, and three coyotes. Here we show that dogs have accumulated nonsynonymous changes in mitochondrial genes at a faster rate than wolves, leading to elevated levels of variation in their proteins. This suggests that a major consequence of domestication in dogs was a general relaxation of selective constraint on their mitochondrial genome. If this change also affected other parts of the dog genome, it could have facilitated the generation of novel functional genetic diversity. This diversity could thus have contributed raw material upon which artificial selection has shaped modern breeds and may therefore be an important source of the extreme phenotypic variation present in modern-day dogs.
|
|
| 6. |
- Borge, Thomas, et al.
(författare)
-
Contrasting patterns of polymorphism and divergence on the Z chromosome and autosomes in two Ficedula flycatcher species
- 2005
-
Ingår i: Genetics. - : Oxford University Press (OUP). - 0016-6731 .- 1943-2631. ; 171:4, s. 1861-1873
-
Tidskriftsartikel (refereegranskat)abstract
- In geographic areas where pied and collared flycatchers (Ficedula hypoleuca and F. albicollis) breed in sympatry, hybridization occurs, leading to gene flow (introgression) between the two recently diverged species. Notably, while such introgression is observable at autosomal loci it is apparently absent at the Z chromosome, suggesting an important role for genes on the Z chromosome in creating reproductive isolation during speciation. To further understand the role of Z-linked loci in the formation of new species, we studied genetic variation of the two species from regions where they live in allopatry. We analyzed patterns of polymorphism and divergence in introns from 9 Z-linked and 23 autosomal genes in pied and collared flycatcher males. Average variation on the Z chromosome is greatly reduced compared to neutral expectations based on autosomal diversity in both species. We also observe significant heterogeneity between patterns of polymorphism and divergence at Z-linked loci and a relative absence of polymorphisms that are shared by the two species on the Z chromosome compared to the autosomes. We suggest that these observations may indicate the action of recurrent selective sweeps on the Z chromosome during the evolution of the two species, which may be caused by sexual selection acting on Z-linked genes. Alternatively, reduced variation on the Z chromosome could result from substantially higher levels of introgression at autosomal than at Z-linked loci or from a complex demographic history, such as a population bottleneck.
|
|
| 7. |
- Cruz, F., et al.
(författare)
-
The legacy of domestication : Accumulation of deleterious mutations in the dog genome
- 2008
-
Ingår i: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 25:11, s. 2331-2336
-
Tidskriftsartikel (refereegranskat)abstract
- Dogs exhibit more phenotypic variation than any other mammal and are affected by a wide variety of genetic diseases. However, the origin and genetic basis of this variation is still poorly understood. We examined the effect of domestication on the dog genome by comparison with its wild ancestor, the gray wolf. We compared variation in dog and wolf genes using whole-genome single nucleotide polymorphism (SNP) data. The d(N)/d(S) ratio (omega) was around 50% greater for SNPs found in dogs than in wolves, indicating that a higher proportion of nonsynonymous alleles segregate in dogs compared with nonfunctional genetic variation. We suggest that the majority of these alleles are slightly deleterious and that two main factors may have contributed to their increase. The first is a relaxation of selective constraint due to a population bottleneck and altered breeding patterns accompanying domestication. The second is a reduction of effective population size at loci linked to those under positive selection due to Hill-Robertson interference. An increase in slightly deleterious genetic variation could contribute to the prevalence of disease in modern dog breeds.
|
|
| 8. |
- Mank, Judith E., et al.
(författare)
-
The unique genomic properties of sex-biased genes: insights from avian microarray data
- 2008
-
Ingår i: BMC Genomics. - : Springer Science and Business Media LLC. - 1471-2164. ; 9, s. 148-
-
Tidskriftsartikel (refereegranskat)abstract
- Background: In order to develop a framework for the analysis of sex-biased genes, we present a characterization of microarray data comparing male and female gene expression in 18 day chicken embryos for brain, gonad, and heart tissue. Results: From the 15982 significantly expressed coding regions that have been assigned to either the autosomes or the Z chromosome ( 12979 in brain, 13301 in gonad, and 12372 in heart), roughly 18% were significantly sex- biased in any one tissue, though only 4 gene targets were biased in all tissues. The gonad was the most sex- biased tissue, followed by the brain. Sex- biased autosomal genes tended to be expressed at lower levels and in fewer tissues than unbiased gene targets, and autosomal somatic sex- biased genes had more expression noise than similar unbiased genes. Sex-biased genes linked to the Z- chromosome showed reduced expression in females, but not in males, when compared to unbiased Z- linked genes, and sex- biased Z- linked genes were also expressed in fewer tissues than unbiased Z coding regions. Third position GC content, and codon usage bias showed some sex- biased effects, primarily for autosomal genes expressed in the gonad. Finally, there were several over-represented Gene Ontology terms in the sex- biased gene sets. Conclusion: On the whole, this analysis suggests that sex- biased genes have unique genomic and organismal properties that delineate them from genes that are expressed equally in males and females.
|
|
| 9. |
- Webster, Matthew T., et al.
(författare)
-
Is there evidence for convergent evolution around human microsatellites?
- 2007
-
Ingår i: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 24:5, s. 1097-1100
-
Tidskriftsartikel (refereegranskat)abstract
- A study by Vowles and Amos (2004) identified atypical patterns of base composition around human microsatellites and argued that microsatellites generate mutational biases in their flanking regions. Here, we perform simulations of molecular evolution using a simple model that suggest similar patterns can be produced without any such biases in genome evolution.
|
|
| 10. |
- Webster, Matthew T, et al.
(författare)
-
Male-driven biased gene conversion governs the evolution of base composition in human alu repeats.
- 2005
-
Ingår i: Mol Biol Evol. - 0737-4038. ; 22:6, s. 1468-74
-
Tidskriftsartikel (refereegranskat)abstract
- Regional biases in substitution pattern are likely to be responsible for the large-scale variation in base composition observed in vertebrate genomes. However, the evolutionary forces responsible for these biases are still not clearly defined. In order to study the processes of mutation and fixation across the entire human genome, we analyzed patterns of substitution in Alu repeats since their insertion. We also studied patterns of human polymorphism within the repeats. There is a highly significant effect of recombination rate on the pattern of substitution, whereas no such effect is seen on the pattern of polymorphism. These results suggest that regional biases in substitution are caused by biased gene conversion, a process that increases the probability of fixation of mutations that increase GC content. Furthermore, the strongest correlate of substitution patterns is found to be male recombination rates rather than female or sex-averaged recombination rates. This indicates that in addition to sexual dimorphism in recombination rates, the sexes also differ in the relative rates of crossover and gene conversion.
|
|
