| 21. |
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| 22. |
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| 23. |
- Berlin, Sofia, et al.
(författare)
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Low mitochondrial variability in birds may indicate Hill-Robertson effects on the W chromosome
- 2007
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Ingår i: Heredity. - : Springer Science and Business Media LLC. - 0018-067X .- 1365-2540. ; 99:4, s. 389-396
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Tidskriftsartikel (refereegranskat)abstract
- Interference among loci subject to selection ( the Hill Robertson effect) may considerably reduce levels of adaptation and variability in genomic regions that lack recombination. Y- or W chromosomes are particularly vulnerable to such effects, since they represent large, non-recombining blocks of genetic material. In birds, the W chromosome and mitochondrial genomes are both maternally transmitted, and hence fail to recombine with each other, whereas in mammals the Y chromosome is paternally transmitted. We show here that mitochondrial DNA sequence diversity is reduced in non-ratite birds compared with mammals. After considering possible confounding factors, such as differences in generation times, mutation rates and demography, we conclude that Hill-Robertson effects associated with the W chromosome provide the most likely explanation for this difference.
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| 24. |
- Berlin, Sofia, et al.
(författare)
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Positive diversifying selection in avian Mx genes
- 2008
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Ingår i: Immunogenetics. - : Springer Science and Business Media LLC. - 0093-7711 .- 1432-1211. ; 60:11, s. 689-697
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Tidskriftsartikel (refereegranskat)abstract
- Mx proteins are interferon-induced GTPases that confer antiviral activities against RNA viruses. We analysed the molecular evolution of the Mx gene in birds using data on interspecific divergence in anseriform and galliform birds, and on intraspecific diversity in commercial chicken lines, local Chinese chicken breeds as well as in the mallard. The overall ratio of non-synonymous to synonymous substitution was unusually high, 0.80, indicating relaxed constraint or positive selection. Evidence for the latter was provided by that a total of 11-18 codons were found to have evolved under positive selection. The great majority of these codons are located in a region unique to birds at the N-terminal end of the Mx protein. We found an excess of non-synonymous polymorphisms relative to synonymous variants in all comparisons. This, together with positive Tajima's D values in the local Chinese chicken breeds and in the mallard suggests that balancing selection is acting in avian Mx genes. As such, Mx mimics the major histocompatibility complex system, indicating that heterozygous individuals are better off withstanding pathogen attack.
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| 26. |
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| 27. |
- Berlin, Sofia, et al.
(författare)
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Testing for adaptive evolution of the female reproductive protein ZPC in mammals, birds and fishes reveals problems with the M7-M8 likelihood ratio test.
- 2005
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Ingår i: BMC Evolutionary Biology. - 1471-2148. ; 5, s. 65-
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Adaptive evolution appears to be a common feature of reproductive proteins across a very wide range of organisms. A promising way of addressing the evolutionary forces responsible for this general phenomenon is to test for adaptive evolution in the same gene but among groups of species, which differ in their reproductive biology. One can then test evolutionary hypotheses by asking whether the variation in adaptive evolution is consistent with the variation in reproductive biology. We have attempted to apply this approach to the study of a female reproductive protein, zona pellucida C (ZPC), which has been previously shown by the use of likelihood ratio tests (LRTs) to be under positive selection in mammals. RESULTS: We tested for evidence of adaptive evolution of ZPC in 15 mammalian species, in 11 avian species and in six fish species using three different LRTs (M1a-M2a, M7-M8, and M8a-M8). The only significant findings of adaptive evolution came from the M7-M8 test in mammals and fishes. Since LRTs of adaptive evolution may yield false positives in some situations, we examined the properties of the LRTs by several different simulation methods. When we simulated data to test the robustness of the LRTs, we found that the pattern of evolution in ZPC generates an excess of false positives for the M7-M8 LRT but not for the M1a-M2a or M8a-M8 LRTs. This bias is strong enough to have generated the significant M7-M8 results for mammals and fishes. CONCLUSION: We conclude that there is no strong evidence for adaptive evolution of ZPC in any of the vertebrate groups we studied, and that the M7-M8 LRT can be biased towards false inference of adaptive evolution by certain patterns of non-adaptive evolution.
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| 28. |
- Berlin, Sofia, 1973-
(författare)
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The Effects of Mutation and Selection on the Rate and Pattern of Molecular Evolution in Birds
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- By comparing sequence diversity and divergence on sex chromosomes one can study how the rate of evolution in affected by mutation and/or selection. The rate of mutation in male biased, meaning that relatively more mutations are created in the male germ line than in the female. Since the male mutation bias (αm) most likely is a consequence of the difference in cell divisions between male and female germ lines, life history characters that affect this difference should covary with αm. Indeed, we found a positive correlation between estimates of αm and increased generation times and increased intensity of sperm competition. We have also found that estimates of αm varied significantly between gametologous introns located on the sex chromosomes. This could be a consequence of the variation in substitution rates between loci. Population genetics theory predicts that both positive and negative selection reduce genetic diversity around a selected locus at a distance determined by the rate of recombination. Consequently, a non-recombining chromosome, like the female specific W chromosome in birds, selection is expected to have a large impact on sequence diversity. Indeed, in a large sequence screening we found only one segregating site among 7643 base pairs sequenced in 47 chicken females. Furthermore, we also found that deleterious substitutions are fixed in a higher rate for W- than Z-linked sequences, which is in agreement with the lack of recombination and strong genetic drift due to the low effective population size. Rarely non-synonymous mutations are beneficial for an individual, but when it happens, the mutation is positively selected and rapidly reaches fixation in a population. We have found that positive selection has been acting on the female reproductive protein, zona pellucida c in birds. This rapid evolution is likely a mechanism to prevent hybridisation.
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| 29. |
- Beuch, Ulrike, et al.
(författare)
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Diversity and evolution of potato mop-top virus
- 2015
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Ingår i: Archives of Virology. - : Springer Science and Business Media LLC. - 0304-8608 .- 1432-8798. ; 160, s. 1345-1351
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Tidskriftsartikel (refereegranskat)abstract
- Nearly complete sequences of RNA-CP and 3'-proximal RNA-TGB were determined for 43 samples of potato mop-top virus (PMTV) originating from potato tubers and field soil from Sweden, Denmark and the USA. The results showed limited diversity and no strict geographical grouping, suggesting only a few original introductions of PMTV from the Andes. Two distinguishable types of RNA-CP and RNA-TGB were found in the samples, but no specific combination of them correlated with spraing symptoms in tubers. Lack of positive selection in the coding sequences indicates that there is no specific molecular adaptation of PMTV to new vectors or hosts.
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| 30. |
- Callesen, Katrine T., et al.
(författare)
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Characterization of Mast Cells from Healthy and Varicose Human Saphenous Vein
- 2022
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Ingår i: Biomedicines. - : MDPI AG. - 2227-9059. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- Mast cells (MCs) are distributed in tissues throughout the body and are highly involved in many physiological and pathophysiological processes. The potential and involvement of different MC phenotypes are still not well understood. MCs are present in blood vessel walls, but their specific phenotypic features are unknown. We aimed at characterizing MCs from human saphenous veins for localization, mediator content, and receptor expression. This was done in MCs from both healthy and varicose human saphenous veins (hSV and vSV, respectively). For both vSV and hSV, we found that vein MCs are mainly present in the tunica adventitia (99% MCs in adventitia) and that the population consists of both MCT and MCTC phenotypes (vSV: 55% MCT, hSV: 64% MCT). The vein MCs contained high levels of histamine (vSV: 27 pg/MC, hSV: 55 pg/MC) and tryptase (vSV: 98 pg/MC, hSV: 111 pg/MC), indicating a strong potential for regulatory effects on blood vessels. The receptor expression of FcɛRI, MRGPRX2, PTAFR, C3aR, and C5aR was found, even though the percentage of positive cells differed between vSV and hSV MCs. We conclude that vein MCs from the blood vessel wall have a high potential to affect the tissue around them.
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