| 1. |
- Backström, Niclas, et al.
(författare)
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Gene conversion drives the evolution of HINTW, an ampliconic gene on the female-specific avian W chromosome.
- 2005
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Ingår i: Mol Biol Evol. - 0737-4038. ; 22:10, s. 1992-9
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Tidskriftsartikel (refereegranskat)abstract
- The HINTW gene on the female-specific W chromosome of chicken and other birds is amplified and present in numerous copies. Moreover, as HINTW is distinctly different from its homolog on the Z chromosome (HINTZ), is a candidate gene in avian sex determination, and evolves rapidly under positive selection, it shows several common features to ampliconic and testis-specific genes on the mammalian Y chromosome. A phylogenetic analysis within galliform birds (chicken, turkey, quail, and pheasant) shows that individual HINTW copies within each species are more similar to each other than to gene copies of related species. Such convergent evolution is most easily explained by recurrent events of gene conversion, the rate of which we estimated at 10(-6)-10(-5) per site and generation. A significantly higher GC content of HINTW than of other W-linked genes is consistent with biased gene conversion increasing the fixation probability of mutations involving G and C nucleotides. Furthermore, and as a likely consequence, the neutral substitution rate is almost twice as high in HINTW as in other W-linked genes. The region on W encompassing the HINTW gene cluster is not covered in the initial assembly of the chicken genome, but analysis of raw sequence reads indicates that gene copy number is significantly higher than a previous estimate of 40. While sexual selection is one of several factors that potentially affect the evolution of ampliconic, male-specific genes on the mammalian Y chromosome, data from HINTW provide evidence that gene amplification followed by gene conversion can evolve in female-specific chromosomes in the absence of sexual selection. The presence of multiple and highly similar copies of HINTW may be related to protein function, but, more generally, amplification and conversion offers a means to the avoidance of accumulation of deleterious mutations in nonrecombining chromosomes.
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| 2. |
- Ceplitis, Helene
(författare)
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Evolutionary dynamics of mitochondrial plasmids in natural populations of Silene vulgaris
- 2002
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Ingår i: Evolution. - : Wiley. - 1558-5646 .- 0014-3820. ; 56:8, s. 1592-1598
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Tidskriftsartikel (refereegranskat)abstract
- Although plasmid-like mitochondrial DNA molecules have been investigated in a number of cultivated plant species, knowledge about their occurrence and behavior in natural plant populations is scarce. In the bladder campion, Silene vulgaris, a common weed of northern Europe, mt-plasmids of three different sizes were detected in a survey of S. vulgaris populations in southern Sweden. Two of the three plasmids usually occurred together within individual plants and showed large variation in frequency between populations. From F-ST-estimates of plasmids, mitochondrial markers, and nuclear markers it was concluded that the plasmids are predominantly maternally inherited in their natural habitat, as observed in greenhouse experiments. The association between mt-plasmids and mitochondrial haplotype was strong, but not complete, in the natural material. These results indicate that the mt-plasmids of S. vulgaris have evolved toward almost strict maternal inheritance.
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| 3. |
- Ceplitis, Helene, et al.
(författare)
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Transmission rates and phenotypic effects of mitochondrial plasmids and cytotypes in Silene vulgaris
- 2002
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Ingår i: Evolution. - : Wiley. - 1558-5646 .- 0014-3820. ; 56:8, s. 1586-1591
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the transmission properties and the phenotypic effects of two mitochondrial plasmids in a population of the bladder campion, Silene vulgaris. In reciprocal crosses between plasmid-free and plasmid-carrying plants, no cases of paternal transmission or loss during maternal transmission were recorded. Neither was any transmission via pollen observed when plasmid-carrying plants of S, vulgaris were used to pollinate plasmid-free plants of the closely related species Silene uniflora. The phenotypic effects of the plasmids were investigated by comparing germination rate, early growth properties, and the gender of plants grown from seeds with and without plasmids. A significant association between plasmid status, on the one hand, and germination propensity and offspring gender, on the other, was found. However, because all plants carrying plasmids in the experiment shared the same cytoplasmic background, the exact contribution of the plasmid to the phenotypic variation could not be determined. Taken together, our experiments show that in S. vulgaris the mt-plasmids are not currently involved in any strong genetic conflict, but that they evolve in close association with their mitochondrial host.
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