Day 70 has 43 protein-coding genes (browser view), including the gene for CPOX (coproporphyrinogen III oxidase.) CPOX is an enzyme that helps build heme, an iron-wielding molecule important for carrying oxygen through the blood and other important chemical processes.
The CPOX protein is part of the nuclear (not mitochondrial) genome and has to get to the mitochondria to do its job. The first amino acids of CPOX (highlighted) are the targeting signal, telling the cell to shuttle it to the mitochondrion.
Click here to see all 8621546 letters of Day 70, with CPOX underlined.