This document discusses DNA microarray analysis and its use in studying Down syndrome. Microarrays allow measurement of expression levels of thousands of genes simultaneously. The analysis process includes importing data, checking for abnormalities, normalizing expression levels, differential analysis between conditions, and filtering results. A case study on Down syndrome is presented, where microarray analysis found increased expression of genes on chromosome 21, including COL6A1, SOD1, CBS, and DYRK1A, consistent with the extra copy of chromosome 21 causing overexpression of genes involved in trisomy 21.