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Chattopadhyay P Pakstis AJ Mukherjee N Iyengar S Odunsi A Okonofua F Bonne-Tamir B Speed W Kidd JR Kidd KK 《European journal of human genetics : EJHG》2003,11(10):760-769
We have constructed haplotypes based on normal variation at six polymorphic sites-five single nucleotide polymorphisms (SNPs) and one short tandem repeat polymorphism (STRP)-at the RET locus for samples of normal individuals from 32 populations distributed across the major continental regions of the world. The haplotyped system spans 41.6 kilobases and encompasses most of the coding region of the gene. All of the markers are polymorphic in all regions of the world and in most individual populations. Expected heterozygosities for the six-site haplotypes range from 82 to 94% for all populations studied except for two Amerindian groups from the Amazon basin at 61 and 76%. Individual populations had from four to eight haplotypes with frequencies exceeding 5%. In general, African, southwest Asian and European groups have the highest numbers of total and of commonly occurring haplotypes; the lowest numbers are observed in Amerindian populations. Overall linkage disequilibrium (LD) for the five SNP sites was very significant (P=0.001) for all the non-African populations, but significant at that level for only one of the seven African populations. In general, the permutation-based xi coefficient that quantifies overall LD tends to increase the farther the population is from Africa, but variability of this measure of LD is often large within geographic regions. Pairwise LD measures among the SNPs also show considerable variation among populations. Association of STRP alleles with the SNP-defined background haplotypes is generally higher outside of Africa than in Africa, but is highly variable. 相似文献
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Common fragile sites (CFSs) are specific genomic regions in normal chromosomes that exhibit genomic instability under DNA replication stress. As replication stress is an early feature of cancer development, CFSs are involved in the signature of genomic instability found in malignant tumors. The landscape of CFSs is tissue‐specific and differs under different replication stress inducers. Nevertheless, the features underlying CFS sensitivity to replication stress are shared. Here, we review the events generating replication stress and discuss the unique characteristics of CFS regions and the cellular responses aimed to stabilizing these regions. 相似文献
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We tested adults and children aged 7 and 14 on the ability to integrate contour elements across variations in the collinearity of the target elements, their spatial proximity, and the relative spacing of the target elements to the background noise elements (Δ). When collinearity was high, the strength of integration for adults was largely independent of spatial proximity and varied only with Δ. It was only when collinearity was less reliable because the orientation of the elements was randomly jittered that spatial proximity began to influence adults’ integration. These patterns correspond well to the probability that real-world contours compose a single object: collinear elements are more likely to reflect parts of a real object and adults integrate them easily regardless of the proximity among those collinear elements. The results from children demonstrate a gradual improvement of contour integration throughout childhood and the slow development of sensitivity to the statistics of natural scenes. Unlike adults, integration in children was limited by spatial proximity regardless of collinearity and one strong cue did not compensate for the other. Only after age 14 did collinearity, the most reliable cue, come to compensate efficiently for spatial proximity. 相似文献
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Behar DM Hammer MF Garrigan D Villems R Bonne-Tamir B Richards M Gurwitz D Rosengarten D Kaplan M Della Pergola S Quintana-Murci L Skorecki K 《European journal of human genetics : EJHG》2004,12(5):355-364
The relative roles of natural selection and accentuated genetic drift as explanations for the high frequency of more than 20 Ashkenazi Jewish disease alleles remain controversial. To test for the effects of a maternal bottleneck on the Ashkenazi Jewish population, we performed an extensive analysis of mitochondrial DNA (mtDNA) hypervariable segment 1 (HVS-1) sequence and restriction site polymorphisms in 565 Ashkenazi Jews from different parts of Europe. These patterns of variation were compared with those of five Near Eastern (n=327) and 10 host European (n=849) non-Jewish populations. Only four mtDNA haplogroups (Hgs) (defined on the basis of diagnostic coding region RFLPs and HVS-1 sequence variants) account for approximately 70% of Ashkenazi mtDNA variation. While several Ashkenazi Jewish mtDNA Hgs appear to derive from the Near East, there is also evidence for a low level of introgression from host European non-Jewish populations. HVS-1 sequence analysis revealed increased frequencies of Ashkenazi Jewish haplotypes that are rare or absent in other populations, and a reduced number of singletons in the Ashkenazi Jewish sample. These diversity patterns provide evidence for a prolonged period of low effective size in the history of the Ashkenazi population. The data best fit a model of an early bottleneck (approximately 100 generations ago), perhaps corresponding to initial migrations of ancestral Ashkenazim in the Near East or to Europe. A genetic bottleneck followed by the recent phenomenon of rapid population growth are likely to have produced the conditions that led to the high frequency of many genetic disease alleles in the Ashkenazi population. 相似文献