Day 4 has the 134 protein-coding genes, more than any day on the p arm of Chromosome 1. However, there are some important non-coding genes here: a cluster of genes that encode snoRNAs (small nucleolar RNAs). The job of these RNAs is to help the nucleolus to make chemical modifications to other RNA molecules.
SNORA73 relatives are found across vertebrates, even the lamprey, implying that the gene’s common ancestor is at least 530 million years old.
Click here to see your SNORA73A gene. Note that, like many other short RNA genes, it is embedded within the intron of a longer gene.