Summary
Highlights
DNA is a polymer consisting of two twisted strands forming a double helix. These strands are held together by chemical bases, whose order forms the genetic code for making proteins. DNA is stored in the nucleus.
DNA is tightly packed into chromosomes. Within a gene, nucleotides A bond with T, and C with G. DNA is wound onto histone proteins to form a DNA histone complex, which then coils and packs into chromatids, held together by a centromere. This structure is only visible during cell division. Mitochondria also contain their own circular DNA, passed from the mother.
An organism's complete set of genetic information is called its genome. The Human Genome Project, an international scientific endeavor, aimed to sequence all 3 billion chemical bases in human DNA. The project began around 1990 and took over a decade to sequence 100,000 genes, though the function of every gene is still not fully understood.
Knowing the order of genes and amino acid sequences in the human genome is crucial for identifying disease-linked genes, developing targeted treatments, understanding and treating inherited genetic disorders, and tracing human migration patterns and evolution by comparing DNA.