The cytoplasmic material of heredity

The chromosome theory of inheritance state that main part of heredity information is in a nucleus, but it is also possible that part of information is in cytoplasmic organelles such as mitochondrion and chloroplast. Such forms of hereditary' are not directed by Mendel’s Laws.

Plants and animals ova have cytoplasm, which is rich in cell organelles, but sperm has very few organelles. So that means that traits which are encoded in cytoplasmic genes are inherited in mother line of pedigree. First to describe cytoplasmic inheritance were German genetics E. Baur and K. Korrens. They did it on example variegated leaf inheritance in some plants.

All hereditary factors localized in cytoplasm are termed plasmotype or plasmon. The unit of cytoplasmic hereditary material same to gene are called plasmogene. It was stated that plastids (plastid’s DNA) and mitochondria (mitochondrion’s DNA) have their own DNA. They are able to self reproduction.

Ріс. 7.9 The cytoplasmic material of herediting: A - the leaf of small tortoise-shell plant; B – the scheme of occasional distribution of green and white plastids in cell division (by С. Соrrens, 1906 and M. E. Lobanov, 1967)

And they are responsible for transmitting cytoplasmic hereditary information. Plastids are self-reproduced organelles of plant cells. They may be inherited by descends only through cytoplasm of mother organism cells. In yeast mitochondria it was detected the genes responsible for respiratory enzymes synthesis. It was shown that these genes are placed in circle DNA molecule of plasmids.

In bacterial cells there are three types of plasmids: containing sex factor F, factor R and factor col - colicinogenic. The bacteria containing F factor are males. They form cytoplasmic bridge toward female cells. Through that bridge, the factor is transmitted to recipient cell during conjugation. That cell becomes male. R factor is responsible for bacteria tolerance to some antibiotics action.

The plasmid with R factor may be transmitted to other cell during conjugation and play an important role in changing bacteria hereditary properties. Colicinogenic plasmids contain special genes which encode special proteins - colicins. Such proteins may kill bacteria of same species without this factor. The material for cytoplasmic inheritance is genes of plasmids, mitochondria and still unknown factors.

The system of cellular genetic apparatus. The system of cellular genetic apparatus includes nucleus genome and cytoplasmic genome. The apparatus is discrete. This apparatus is presented by chromosomes and their genes in nucleus and by plasmogenes of organelles in the cytoplasm.