Nuclear DNA is the DNA inside the cell nucleus of eukaryotic cells. This DNA is a double helix, with two strands wound around each other. This double helix structure was first described by Francis Crick and James D. Watson in 1953.
This DNA is different from the DNA in bacteria, mitochondria and plastids such as chloroplasts. Nuclear DNA is very long, and is bound up in chromosomes which, apart from the DNA, are protein structures. The second difference is that each eukaryote cell has two sets of DNA, one set from each parent: it is diploid. Mitochondrial and plastid DNA is relatively short, is in a circle, and there is only one set (haploid), not two. It is supposed that these organelles were once independent bacteria (see endosymbiosis).
The consequence of nuclear DNA being double is highly important. The genes in mitochondria and plastids only change when a mutation happens. Nuclear DNA gets shuffled by the cell division known as meiosis, part of sexual reproduction. This leads to a variety of offspring from any two parents.
Another feature of nuclear DNA is that it is regulated by proteins and RNA systems which control the rate of transcription into messenger RNA. In this way, most of the cell products are adjusted according to the circumstances.