with RNA, the sequence determines the shape, as bases from one part of the strand find bases in another part with which to pair.

In prebiotic times—that is, before the emergence of the first life-form—the bricks would have to form spontaneously from chemicals present in the environment.

all these self-splicing RNAs

long before CRISPR, scientists had found that they could easily trick homologous recombination by introducing‡ a donor template DNA that matched the sequences near where a break had occurred but included a patch of nonmatching DNA farther away.

Stem cells divide asymmetrically,

With a sequence complementary to that of the codon, this triplet is called the anticodon.

Because almost all enzymes are proteins and have no RNA, they are unfazed by RNase treatment.

But in humans, the introns turned out to be more than just an annoyance. They are quite useful. They give RNA wiggle room to splice the code in more than one way, resulting in a wide repertoire of potential proteins from the same set of genes.

interference (RNAi).