Since chloroplasts and mitochondria are organelles found in the cytoplasm, outside the nucleus, they are often transmitted with the cytoplasm. As discussed earlier, during sexual reproduction most of the cytoplasm in the zygote is derived from the egg (female parent), so that one expects that organellar DNA is maternally transmitted. Besides the relatively predominant inputs of cpDNA and mtDNA from the female parent to the zygote, the inheritance of cpDNA and mtDNA is also influenced by vegetative sorting and by differences in rates of replication of organellar DNAs derived from the two parents. This leads to elimination of paternal cpDNA and paternal mtDNA leading to maternal inheritance. For many years now, the cpDNA in angiosperms is known to be either maternally inherited or biparentally inherited. In contrast to this till recently, mtDNA in angiosperms and in animals was known to be strictly maternally inherited.

Only in late 1980s and early 1990s, partly due to the use of backcrosses to male parent, for increasing the concentration and partly due to the availability of RFLP and PCR techniques (see Genetic Engineering and Biotechnology 1.  Recombinant DNA and PCR (Cloning and Amplification of DNA)) examples of paternal and biparental inheritance of mtDNA both in plants and animals became available. For cpDNA also, several studies in conifers (Gymnosperms), conducted during late 1980s and early 1990s, revealed strictly paternal inheritance, only few offspring having maternal or novel genotypes. Paternal transmission of cpDNA and mtDNA, using specific molecular makers, has been shown for many cases including the following : (i) In barley-rye intergeneric crosses, some paternal inheritance of mtDNA was observed, (ii) In alfalfa, biparental inheritance of mtDNA was observed, (iii) In intraspecific crosses of Douglas fir (Pseudotsuga menziesii), as well as in interspecific crosses in the genera, Pinus, Larix and Picea, strictly paternal inheritance of cpDNA was observed, (iv) In two intraspecific crosses of redwood {Sequoia sempervirens), both cpDNA and mtDNA were strictly paternally inherited (as shown by using specific chloroplast DNA probes derived from Petunia and mitochondrial DNA probes derived from maize), (v) In an interspecific cross in mice (Mus domesticus x M. spretus), where concentration of paternal mtDNA was increased by backcrossing, paternal mtDNA was transferred at a rate of 10^-4 relative to maternal mtDNA (as shown by amplification of paternal mtDNA using polymerase chain reaction), (vi) In hybrid crosses in Drosophila also, incidental paternal transmission of mtDNA was reported, (vii) In 1991, interspecific crosses (Mytilus edulis x M. trossulus)and intraspecific crosses in mussels (a mollusc, like Unio)were used to demonstrate extensive contribution of paternal mtDNA.