In a standard DNA double helix, adenine pairs with thymine and cytosine with guanine. The two strands are complementary and run in opposite chemical directions. They are not mirror images or photographic negatives.

Base pairing lets each old strand guide synthesis of a new partner during replication. The cell does much more than "simply unzip": enzymes open, copy, proofread, repair and rejoin DNA. The elegance lies in a chemical structure that permits both fidelity and change.

The DNA in a diploid human cell would extend to roughly two metres if laid end to end, yet most of it occupies a nucleus only micrometres across. In eukaryotic cells, DNA winds around histone proteins to form nucleosomes, which fold into chromatin at several scales. Supercoiling also matters, but it is not another name for all chromatin packaging.

Compression is only half the achievement. The packed genome must still be copied, repaired and selectively made accessible. It is less like a book squeezed shut than a library continually rearranged while readers are inside.

Every genome arrives through a lineage, but not as one unbroken molecular thread. DNA molecules are copied, recombined and sometimes altered; the physical molecules in one generation are not immortal objects passed intact from the first cells.

What persists is patterned descent with modification. Some sequences are deeply conserved, others are recent, and much of a genome has no simple story as an adaptive "strategy." The wonder is not perfect memory. It is continuity spacious enough to include error, loss and novelty.

Raymond Gosling made Photo 51 in Rosalind Franklin's research group: an X-ray diffraction image of the B form of DNA whose cross-shaped pattern carried strong helical clues. Maurice Wilkins showed the image to Watson without Franklin's knowledge. Watson and Crick also received values from an internal report containing her work.

Those facts matter, but a single stolen-picture plot can hide Franklin's larger contribution as a scientist with her own analysis, as well as the work of Gosling, Wilkins, Stokes, Wilson, Chargaff and others. Nature published three DNA papers together in April 1953. Credit is not made more honest by reducing a collaborative and unequal history to one prop.

DNA can be sequenced as an alphabet of four bases, and cells use nucleotide triplets in translating RNA into protein. The language of information made powerful experiments possible. It remains an analogy with limits.

A genome is a chemical participant in a cell, read differently across tissues and environments. A mutation may be harmful, helpful or neutral; a virus is an evolving biological entity, not merely "bad code." We are neither magic nor data alone. Meaning arises through molecules acting in cells, bodies and worlds.