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Down syndrome is caused by an extra copy of all or part of chromosome 21; it is the most common non-lethal trisomy in humans. The At the time of the study used in this tutorial, conflicting reports had thrown into doubt whether individuals with Down syndrome have dysregulation of gene expression throughout the genome or primarily in genes from chromosome 21. This study revealed a significant upregulation of chromosome 21 genes at the gene expression level in individuals with Down syndrome; this dysregulation was largely specific to chromosome 21 only and not to any other chromosomes. This experiment a genome-wide phenomenon. This gene expression analysis for this study was performed using the Affymetrix GeneChip™ Human U133A arrays. It includes 25 samples taken from 10 human subjects and 4 different tissues.

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