Day 181 has 117 protein-coding genes (browser view) and is my favorite day of Genome Year. It is the home of the red- and green-sensitive opsin genes, so it is the source of X-linked red-green colorblindness; and it is the home to the first and most-replicated locus associated with sexual orientation, a highly-heritable trait.
Click here to see all 8668939 letters of Day 181 with opsin gene OPN1LW underlined.