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Positive selection and sequence rearrangements generate extensive polymorphism in the gamete recognition protein bindin 总被引:15,自引:12,他引:15
Bindin is a gamete recognition protein of sea urchins that mediates
species-specific attachment of sperm to an egg-surface receptor during
fertilization. Sequences of bindin from closely related urchins show fixed
species-specific differences. Within species, highly polymorphic bindin
alleles result from point substitution, insertion/deletion, and
recombination. Since speciation, positive selection favoring allelic
variants has generated diversity in bindin polypeptides. Intraspecific
bindin variation can be tolerated by the egg receptor, which suggests
functional parallels between this system and other flexible recognition
systems, including immune recognition. These results show that polymorphism
in mate recognition loci required for rapid evolution of sexual isolation
can arise within natural populations.
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Esophageal cancer involves multiple genetic alternations. A systematic codon usage bias analysis was completed to investigate the bias among the esophageal cancer responsive genes. GC-rich genes were low (average effective number of codon value was 49.28). CAG and GTA are over-represented and under-represented codons, respectively. Correspondence analysis, neutrality plot, and parity rule 2 plot analysis confirmed the dominance over mutation pressure in modulating the codon usage pattern of genes linked with esophageal cancer. 相似文献
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Tallury SP Hilu KW Milla SR Friend SA Alsaghir M Stalker HT Quandt D 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2005,111(7):1229-1237
Section Arachis is the largest of nine sections in the genus Arachis and includes domesticated peanut, A. hypogaea L. Most species are diploids (x=10) with two tetraploids and a few aneuploids. Three genome types have been recognized in this section (A, B and D), but
the genomes are not well characterized and relationships of several newly described species are uncertain. To clarify genomic
relationships in section Arachis, cytogenetic information and molecular data from amplified fragment length polymorphism (AFLP) and the trnT-F plastid region were used to provide an additional insight into genome composition and species relationships. Cytogenetic
information supports earlier observations on genome types of A. cruziana, A. herzogii, A. kempff-mercadoi and A. kuhlmannii but was inconclusive about the genome composition of A. benensis, A. hoehnei, A. ipaensis, A. palustris, A. praecox and A. williamsii. An AFLP dendrogram resolved species into four major clusters and showed A. hypogaea grouping closely with A. ipaensis and A. williamsii. Sequence data of the trnT-F region provided genome-specific information and showed for the first time that the B and D genomes are more closely related
to each other than to the A genome. Integration of information from cytogenetics and biparentally and maternally inherited
genomic regions show promise in understanding genome types and relationships in Arachis. 相似文献
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Protein evolution in different cellular environments: cytochrome b in sharks and mammals 总被引:4,自引:0,他引:4
DNA sequences for the mitochondrial cytochrome b gene were determined for
13 species of sharks. Rates and patterns of amino acid replacement are
compared for sharks and mammals. Absolute rates of cytochrome b evolution
are six times slower in sharks than in mammals. Bivariate plots of the
number of nonsynonymous and silent transversions are indistinguishable in
the two groups, however, suggesting that the differences in amino acid
replacement rates are due primarily to differences in DNA substitution
rates. Patterns of amino acid replacement are also similar in the two
groups. Conserved and variable regions occur in the same parts of the
cytochrome b gene, and there is little evidence that the types of amino
acid changes are significantly different between the groups. Similarity in
the relative rates and patterns of protein change between the two groups
prevails despite dramatic differences in the cellular environments of
sharks and mammals. Poor penetrance of physiological differences through to
rates of protein evolution provides support for the neutral theory and
suggests that, for cytochrome b, patterns of evolution have been relatively
constant throughout much of vertebrate history.
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The simple repeat poly(dT-dG).poly(dC-dA) common to eukaryotes is absent from eubacteria and archaebacteria and rare in protozoans 总被引:5,自引:0,他引:5
Genomic DNA from a wide variety of prokaryotic and eukaryotic organisms has
been assayed for the simple repeat sequence poly(dT-dG).poly(dC-dA) by
Southern blotting and DNA slot blot hybridizations. Consistent with
findings of others, we have found the simple alternating sequence to be
present in multiple copies in all organisms in the animal kingdom (e.g.,
mammals, reptiles, amphibians, fish, crustaceans, insects, jellyfish,
nematodes). The TG element was also found in lower eukaryotes
(Saccharomyces cerevisiae, Neurospora crassa, and Dictyostelium discoideum)
and at a much lower frequency in protozoans (Oxytricha fallux and
Tetrahymena thermophila). The sequence was also repeated in high copy
number in a higher plant (Zea mays) as well as at very high levels in a
unicellular green alga (Chlamydomonas reinhardi). Although the copy number
of the repeat per haploid genome was generally proportional to genome size,
there was a greater-than-1,000-fold variation in the number of
(TG)25/100-kb genomic DNA. By contrast, no eu-or archaebacterium--including
Myxococcus xanthus, whose life cycle is very similar to that of the slime
mold Dictyostelium discoideum, and Halobacter volcanii, whose genome
contains other repeated sequences-- was found whose genomic DNA contained
this sequence in detectable amounts. A computer search also failed to find
the TG element in human mitochondrial DNA.
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