Genes are made up of DNA, which is shaped like a twisted ladder with rungs made of molecules called nucleotide bases linked in specific pairs. The arrangement of bases along the DNA provides the cell with instructions on making proteins and other molecules that control cellular processes. DNA is coiled into rod-shaped structures called chromosomes, which are stored in the nucleus of the cell. Humans have 22 pairs of chromosomes (called autosomes) plus two sex chromosomes.
Structure: Mitochondrial DNA
Mitochondria (energy-producing structures in cells) contain a small amount of DNA. Unlike DNA in the cell nucleus, which is inherited from both parents, mitochondrial DNA is inherited only from the mother. Mistakes in mitochondrial DNA are known to be the cause of several disorders.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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