The Body · Bjarni Kristján Leifsson

CHAPTER I THE CODE

01 THE CODE

SHOW

Drag the body to turn it — flick and it keeps spinning. Scroll to come closer, click any structure to name it, double-click to put it back.

Start at the bottom. Four letters — adenine, thymine, guanine, cytosine — pairing A to T and G to C, twisted into a ladder two nanometres wide that turns once every ten and a half rungs. Two metres of it is wound into every cell: around spools of protein, into fibres, into 46 chromosomes. 3.1 billion letters, and the ends are capped with telomeres that shorten a little at every copy.

3.1 bn: letters in one copy of the genome
2 m: of DNA wound into every single cell
~20,000: protein-coding genes — about 1.5% of it
2 nm: across; one full turn every 10.5 rungs

Four letters, two pairs

Adenine pairs with thymine across two hydrogen bonds; guanine pairs with cytosine across three. That is the whole alphabet. Because the pairing is fixed, either strand contains the full message — which is how a cell copies it, and how it repairs a strand that has been damaged.

How two metres fits in a cell

The helix winds twice around a spool of eight histone proteins to make a nucleosome, nucleosomes coil into a 30-nanometre fibre, and the fibre folds into loops and domains. At division it condenses further into the 46 chromosomes you can see under a microscope. Which stretches are wound tight and which are left open is most of what makes a liver cell different from a neuron — same text, different pages open.

The ends run down

Chromosome ends are capped with telomeres, a repeated sequence that is not a gene. A little is lost at every copy, so a cell has a finite number of divisions in it. Sperm, egg and stem cells carry telomerase to rebuild the cap; most cancers switch it back on, which is part of what makes them immortal.

Most of it is not genes

Protein-coding sequence is about 1.5% of the genome. Much of the rest is regulatory — switches, spacers, promoters — and a large part is repeated elements and viral remnants. 'Junk DNA' was always a placeholder for 'we do not know yet', and a good deal of it turned out to be control.

Where the research is

Information only · not medical advice · nothing here is a recommendation · talk to a doctor

CRISPR gene editingAPPROVED

What it is A guided molecular cut-and-repair system. The first CRISPR therapy, for sickle-cell disease and beta-thalassaemia, was approved in late 2023 — cells are taken out, edited, and returned.

What to expect In those two diseases the results have been dramatic and durable. It is one edit, one tissue, one condition at a time; it is not a way to edit a person who is already grown.

The catch Off-target edits, delivery into the right tissue, and cost measured in millions per patient are the live problems. Editing embryos remains prohibited in most of the world.

Gene therapyAPPROVED

What it is Delivering a working copy of a gene, usually inside a modified virus. Approved for spinal muscular atrophy, some inherited blindness, haemophilia and others.

What to expect For single-gene diseases with a known culprit, sometimes a one-off cure. For anything caused by hundreds of genes interacting, no.

Polygenic risk scoresMIXED

What it is Adding up thousands of small genetic effects to estimate your risk of a common condition.

What to expect Useful at population scale and for research. For one person they shift the odds modestly and are much less accurate outside the ancestry group they were trained on.

The catch Sold direct to consumers with more confidence than the numbers support.

What am I watching?

An anatomy study, drawn live. The body is a real anatomical scan — skin, skeleton, every major muscle group, the organs, the arterial and venous trees, brain and cord — lit and shaded in tissue colour. Switch any layer on or off above, and open the Atlas to turn the body and click a structure by name. Only the molecules, the labels and the closing Vitruvian figure are drawn by hand. Figures are real, rounded and typical for an adult — this is a drawing, not medical advice.