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竹叶眼子菜(Potamogeton malaianus)、微齿眼子菜(Potamogeton maackianus)、苦草(Vallisneria spiralis)、穗花狐尾藻(Myriophyllum spicatum)、黑藻(Hydrilla verticillata)是长江中下游湖泊主要的沉水植物。在栽培条件下,它们的无性繁殖速率(单位时间内新增个体数)大小顺序为黑藻>微齿眼子菜>竹叶眼子菜>苦草>穗花狐尾藻。同时采用抛掷实验的方法观察研究了这5种沉水植物及其无性繁殖体的存活和生根情况;完整植株存活率为黑藻>穗花狐尾藻>微齿眼子菜>竹叶眼子菜>苦草,无性繁殖体部分存活率为黑藻>苦草>穗花狐尾藻>微齿眼子菜>竹叶眼子菜。生根能力和其存活时间长短相关,而且生根能力与存活率大小基本一致。在实验中,只有穗花狐尾藻的断枝存活率和生根能力存在差异,故无性繁殖体生根能力为黑藻>苦草>微齿眼子菜>竹叶眼子菜>穗花狐尾藻。 相似文献
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Intraspecific nuclear DNA variation in Drosophila 总被引:18,自引:6,他引:12
We have summarized and analyzed all available nuclear DNA sequence
polymorphism studies for three species of Drosophila, D. melanogaster (24
loci), D. simulans (12 loci), and D. pseudoobscura (5 loci). Our major
findings are: (1) The average nucleotide heterozygosity ranges from about
0.4% to 2% depending upon species and function of the region, i.e., coding
or noncoding. (2) Compared to D. simulans and D. pseudoobscura (which are
about equally variable), D. melanogaster displays a low degree of DNA
polymorphism. (3) Noncoding introns and 3' and 5' flanking DNA shows less
polymorphism than silent sites within coding DNA. (4) X-linked genes are
less variable than autosomal genes. (5) Transition (Ts) and transversion
(Tv) polymorphisms are about equally frequent in non-coding DNA and at
fourfold degenerate sites in coding DNA while Ts polymorphisms outnumber Tv
polymorphisms by about 2:1 in total coding DNA. The increased Ts
polymorphism in coding regions is likely due to the structure of the
genetic code: silent changes are more often Ts's than are replacement
substitutions. (6) The proportion of replacement polymorphisms is
significantly higher in D. melanogaster than in D. simulans. (7) The level
of variation in coding DNA and the adjacent noncoding DNA is significantly
correlated indicating regional effects, most notably recombination. (8)
Surprisingly, the level of polymorphism at silent coding sites in D.
melanogaster is positively correlated with degree of codon usage bias. (9)
Three proposed tests of the neutral theory of DNA polymorphisms have been
performed on the data: Tajima's test, the HKA test, and the
McDonald-Kreitman test. About half of the loci fail to conform to the
expectations of neutral theory by one of the tests. We conclude that many
variables are affecting levels of DNA polymorphism in Drosophila, from
properties of nucleotides to population history and, perhaps, mating
structure. No simple, all encompassing explanation satisfactorily accounts
for the data.
相似文献
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Caccone A; Moriyama EN; Gleason JM; Nigro L; Powell JR 《Molecular biology and evolution》1996,13(9):1224-1232
Drosophila melanogaster belongs to a closely related group of eight species
collectively known as the melanogaster subgroup; all are native to
sub-Saharan Africa and islands off the east coast of Africa. The
phylogenetic relationships of most species in this subgroup have been well
documented; however, the three most closely related species, D. simulans,
D. sechellia, and D. mauritiana, have remained problematic from a
phylogenetic standpoint as no data set has unambiguously resolved them. We
present new DNA sequence data on the nullo and Serendipity-alpha genes and
combine them with all available nuclear DNA sequence data; the total data
encompass 12 genes and the ITS of rDNA. A methodological problem arose
because nine of the genes had information on intraspecific polymorphisms in
at least one species. We explored the effect of inclusion/exclusion of
polymorphic sites and found that it had very little effect on phylogenetic
inferences, due largely to the fact that 82% of polymorphisms are
autapomorphies (unique to one species). We have also reanalyzed our
previous DNA-DNA hybridization data with a bootstrap procedure. The
combined sequence data set and the DNA-DNA hybridization data strongly
support the sister status of the two island species, D. sechellia and D.
mauritiana. This at least partially resolves what had been a paradox of
parallel evolution in these two species.
相似文献
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Yaqin Xu Christine Tertilt Anja Krause Luis EN Quadri Ronald G Crystal Stefan Worgall 《Respiratory research》2009,10(1):26
Background
Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Infections of the respiratory tract are a hallmark in CF. The host immune responses in CF are not adequate to eradicate pathogens, such as P. aeruginosa. Dendritic cells (DC) are crucial in initiation and regulation of immune responses. Changes in DC function could contribute to abnormal immune responses on multiple levels. The role of DC in CF lung disease remains unknown.Methods
This study investigated the expression of CFTR gene in bone marrow-derived DC. We compared the differentiation and maturation profile of DC from CF and wild type (WT) mice. We analyzed the gene expression levels in DC from naive CF and WT mice or following P. aeruginosa infection.Results
CFTR is expressed in DC with lower level compared to lung tissue. DC from CF mice showed a delayed in the early phase of differentiation. Gene expression analysis in DC generated from naive CF and WT mice revealed decreased expression of Caveolin-1 (Cav1), a membrane lipid raft protein, in the CF DC compared to WT DC. Consistently, protein and activity levels of the sterol regulatory element binding protein (SREBP), a negative regulator of Cav1 expression, were increased in CF DC. Following exposure to P. aeruginosa, expression of 3β-hydroxysterol-Δ7 reductase (Dhcr7) and stearoyl-CoA desaturase 2 (Scd2), two enzymes involved in the lipid metabolism that are also regulated by SREBP, was less decreased in the CF DC compared to WT DC.Conclusion
These results suggest that CFTR dysfunction in DC affects factors involved in membrane structure and lipid-metabolism, which may contribute to the abnormal inflammatory and immune response characteristic of CF. 相似文献18.
用抗性筛选法选育γ—亚麻酸(GLA)高产菌株 总被引:13,自引:0,他引:13
以深黄被孢霉(Mortierella isabellina)为出发菌株,经紫外线诱变处理,采用抗性筛选法,直接在梯度平板上挑选取抗脂肪酸脱氢酶抑制物抑芽丹(maleic hydrazide)的菌株进行初筛,然后经摇瓶发酵法测定相关性能指标进行得筛,获得一株生产性能比出发菌株显提高的突变株M80,其菌体收率达25.10g/L、油脂产率达12.35g/L、γ-亚麻酸(GLA)产率达771.88mg/L。 相似文献
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Horizontal transmission, vertical inactivation, and stochastic loss of mariner-like transposable elements 总被引:13,自引:5,他引:8
Horizontal transmission has been well documented as a major mechanism for
the dissemination of mariner-like elements (MLEs) among species. Less well
understood are mechanisms that limit vertical transmission of MLEs
resulting in the "spotty" or discontinuous distribution observed in closely
related species. In this article we present evidence that the genome of the
common ancestor of the melanogaster species subgroup of Drosophila
contained an MLE related to the mellifera (honey bee) subfamily. Horizontal
transmission, approximately 3-10 MYA, is strongly suggested by the
observation that the sequence of the MLE in Drosophila erecta is 97%
identical in nucleotide sequence with that of an MLE in the cat flea,
Ctenocephalides felis. The D. erecta MLE has a spotty distribution among
species in the melanogaster subgroup. The element has a high copy number in
D. erecta and D. orena, a moderate copy number in D. teissieri and D.
yakuba, and was apparently lost ("stochastic loss") in the lineage leading
to D. melanogaster, D. simulans, D. mauritiana, and D. sechellia. In D.
erecta, most copies are concentrated in the heterochromatin. Two copies
from D. erecta, denoted De12 and De19, were cloned and sequenced, and they
appear to be nonfunctional ("vertical inactivation"). It therefore appears
that the predominant mode of MLE evolution is vertical inactivation and
stochastic loss balanced against occasional reinvasion of lineages by
horizontal transmission.
相似文献
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