Jeffery M Trent | PubMed Health

PubMed2007

Germline copy number polymorphisms involving larger than 100 kb are uncommon in normal subjects.

BACKGROUND: Recent studies using ROMA and Array-CGH suggest that germline copy number polymorphisms (CNPs) involving >100 kb are common in humans. METHODS: In this study, we used the Affymetrix GeneChip 100K single nucleotide polymorphisms (SNP) mapping panel to further examine the type and frequency of germline CNPs in the genome. By utilizing the allele intensity data generated while genotyping approximately 116,000 SNPs among 23 subjects from 4 families, we were able to detect multiple CNPs. RESULTS: However, in contrast to several previous studies, we found that CNPs >100 kb are rare in the genome but CNPs involving 100s-1,000s of base pairs are more common. CONCLUSIONS: We have demonstrated the utility of this approach, which has an important advantage over other methods because it is able to simultaneously assess both CNPs and SNPs, and therefore has great potential in genetic association studies of common diseases.

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PubMed2002

Ratio statistics of gene expression levels and applications to microarray data analysis.

MOTIVATION: Expression-based analysis for large families of genes has recently become possible owing to the development of cDNA microarrays, which allow simultaneous measurement of transcript levels for thousands of genes. For each spot on a microarray, signals in two channels must be extracted from their backgrounds. This requires algorithms to extract signals arising from tagged mRNA hybridized to arrayed cDNA locations and algorithms to determine the significance of signal ratios. RESULTS: This paper focuses on estimation of signal ratios from the two channels, and the significance of those ratios. The key issue is the determination of whether a ratio is significantly high or low in order to conclude whether the gene is upregulated or downregulated. The paper builds on an earlier study that involved a hypothesis test based on a ratio statistic under the supposition that the measured fluorescent intensities subsequent to image processing can be assumed to reflect the signal intensities. Here, a refined hypothesis test is considered in which the measured intensities forming the ratio are assumed to be combinations of signal and background. The new method involves a signal-to-noise ratio, and for a high signal-to-noise ratio the new test reduces (with close approximation) to the original test. The effect of low signal-to-noise ratio on the ratio statistics constitutes the main theme of the paper. Finally, and in this vein, a quality metric is formulated for spots. This measure can be used to decide whether or not a spot ratio should be deleted, or to adjust various measurements to reflect confidence in the quality of the measurement. CONTACT: e-dougherty@tamu.edu

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