Gene categorization by phenotype penetrance. Genes are grouped in three categories, according to P value (Wilcoxon test) and the tissues in which they were tested. The first category (left) shows genes with P < 0.01, meaning that the expression levels in Ts65Dn individual mice are consistently different from euploids. The second category shows genes with 0.01 <P < 0.05, for which the expression levels of Ts65Dn samples partially overlap with euploids. The last category (P > 0.05) groups genes for which the expression levels between Ts65Dn and euploid mice cannot be distinguished. Genes in the first category might be responsible for the fully penetrant signs in trisomy, genes in the second could contribute to the variable signs, whereas the third category contains genes that may make little or no contribution.