During evolution, the mitochondria have retained their own genome, which, although very small compared to that of a bacterium, is essential for the proper functioning of these organelles. Confined within the mitochondria, organelles that produce cellular energy, the mitochondrial genome (mtDNA) is distinct from the DNA in the nucleus. The transmission of this DNA is generally called non-Mendelian because it is only transmitted by the mother.
Chloroplasts contain DNA grouped into nucleoids; each chloroplast can contain up to 100 copies of the genome. The DNA molecules of the chloroplast genome are generally linear or branched. The chloroplast genome is very small, 37 to 220 kb and usually contains about a hundred genes
