http://www.crg.eu/en/news/sperm-tail-may-determine-semen-quality Day 268 has 48 protein-coding genes (browser view), including SPERT (spermatid-associated protein).
SPERT is an example of a gene whose product is only known through its localization. SPERT is expressed only in sperm while their tails are growing.
Click here to see all 8168881 letters of Day 268 with SPERT underlined.