The
chloroplast genome It is now known that the
chloroplasts of plants carry their genetic information in the form of small circular DNA molecules, similar in size and form to the
chromosomes of bacteria . These DNA
molecules contain
genes which code for some of the proteins and RNAs used in chloroplast structure and function; and it is mutations in these genes which are most likely to be responsible for the leaf variegation effects described above. It must also be emphasised that chloroplasts are not totally independent of the
nucleus in their heredity; most of their proteins are coded by nuclear genes, and mutations in these show normal Mendelian patterns of inheritance. The DNA molecules which make up the chloroplast genome are ‘naked’ ones and bear no resemblance to the chromosomes of the nucleus , which are much larger and are composed of both protein and DNA .The really surprising thing about the chloroplast DNA is the large number of copies which are present: up to 300 in a mature plastid. Since an average of 160 chloroplasts are present in a mesophyll cell of the mature leaf of a cereal such as wheat, this means that there may be as many as 48 000 chloroplast ‘chromosomes’ per mesophyll cell. The reason for this enormous redundancy of genetic information is unknown.
More abstracts about the chloroplast genome