Genetics studies genes; genomics studies the whole book
For most of the 20th century, genetics worked one gene at a time. You picked a trait, traced it through families, and slowly mapped a single gene to a place on a chromosome. That careful, gene-by-gene approach is the heart of classical genetics. Genomics is what happens when you zoom all the way out and study the *entire* set of DNA in an organism at once — every gene, plus all the stretches between them.
A genome is that complete DNA library — the full sequence of letters carried in one set of an organism's chromosomes. For a human, that is about 3.2 billion base pairs. Genomics asks questions you simply cannot ask one gene at a time: How many genes are there in total? How do they compare across species? Which letters differ between two people, and do those differences matter?
What a genome actually contains
Here is a surprise that genomics revealed: genes are a small minority of the genome. Of those 3.2 billion letters, only about 1–2% are protein-coding DNA. The rest is non-coding DNA — regulatory switches, RNA genes, repeats, spacers, and sequence whose job we are still working out. Reading the whole genome forces you to take all of it seriously, not just the famous coding bits.
Human genome at a glance ------------------------------------- Total length ~3,200,000,000 bp Protein-coding genes ~20,000 Coding DNA ~1-2% of the genome Non-coding DNA ~98% Chromosomes 22 autosomes + X + Y ------------------------------------- Reading 1 letter per second, nonstop, would take you about 100 years.
The leap from genetics to genomics only became possible once we could read DNA letters quickly and cheaply. The story of the rest of this track is the story of genome sequencing: how we turn a physical molecule into a string of A, C, G, and T you can store, search, and compare. The landmark first attempt to read an entire human genome — the Human Genome Project — is where the next guide begins.