DNA, or deoxyribonucleic acid, is the molecular blueprint that underpins all life. These double‑helical molecules encode the instructions that govern cellular function, development, and inheritance in every living organism.
Each human inherits one complete set of genes from the mother and one from the father. Genes—sequences of nucleotides—carry the information that shapes everything from skin tone to cognitive ability. The human genome comprises roughly 30,000 genes distributed across 46 chromosomes, with each chromosome housing fewer than 1,000 genes.
In the cell nucleus, DNA is compacted into 23 pairs of chromosomes. The first 22 pairs—autosomes—are identical in size, shape, and genetic content between the sexes. The 23rd pair are the sex chromosomes, which determine biological sex: two X chromosomes produce female cells, whereas an X and a Y chromosome produce male cells.
Four nitrogenous bases—adenine (A), thymine (T), cytosine (C), and guanine (G)—form the genetic code. Complementary base pairing (A‑T and C‑G) creates the rungs of the DNA double helix, while phosphate and deoxyribose sugar molecules form the backbone. This ladder‑like structure allows DNA to store and transmit vast amounts of genetic information.
Accurate DNA replication is essential for cell division. Each strand of the double helix serves as a template, ensuring that every new cell inherits a faithful copy of the genome. This mechanism preserves the integrity of the hereditary blueprint across generations.
While the human genome is 99 % identical across individuals, no two people share an identical sequence—except in the rare case of monozygotic twins. Compared to our closest living relatives, the chimpanzee, humans share about 96 % of their DNA, yet still differ by roughly 40 million base pairs.
