Molecular Biology

To assess genomic variation, it is possible to identify the single nucleotide polymorphisms (SNP) which an individual carries. Using the Affymetrix Genome-wide Human SNP Assay, it is possible to assess 906,600 SNPs on a single array. This protocol, the next iteration of the GeneChip Mapping 500K array set, is based directly on the manufacturers’ protocol and shows steps which are highly similar to that which is found here: http://media.affymetrix.com/support/downloads/manuals/genomewidesnp6_manual.pdf.

This protocol describes how to build a gene network based on the graphical Gaussian model (GGM) from large scale microarray data. GGM uses partial correlation coefficient (pcor) to infer co-expression relationship between genes. Compared to the traditional Pearson’ correlation coefficient, partial correlation is a better measurement of direct dependency between genes. However, to calculate pcor requires a large number of observations (microarray slides) greatly exceeding the number of variables (genes). This protocol uses a regularized method to circumvent this obstacle, and is capable of building a network for ~20,000 genes from ~2,000 microarray slides. For more details, see Ma et al. (2007). For help regarding the script, please contact the author.