CYTOPLASMIC INHERITANCE

From Big Medical Encyclopedia

CYTOPLASMIC INHERITANCE (grech, kytos a receptacle, a cell + plasma molded, issued; synonym: not Mendelian heredity, heredity plasmatic, extrachromosomal inheritance, not chromosomal heredity, extranuclear heredity) — transfer to posterity of the separate signs and properties caused by not chromosomal (cytoplasmatic) successive structural elements of a cell. This process is made partially independently, partially — depending on a cellular kernel.

N of c., unlike Mendelian heredity (see. Mendel laws ), it is characterized by the fact that cytoplasma hereditary factors — cytoplasmatic genes, or plasmogenes, make a plasmon and are not split, and are transferred to all posterity in the one-parent way. Since the ovum contains cytoplasms many times more, than spermiya, at merge of both gametes the female gamete makes a much bigger contribution to cytoplasm of a zygote, than men's. Therefore practically all cytoplasmatic genes are transferred to posterity on the maternal line.

Carry to the successive structural elements of cytoplasm which are carriers of plasmogenes mitochondrions (see) all eukaryotes, i.e. organisms, cells to-rykh contrary to prokariota contain the typical kernel surrounded with a membrane and also chlorolayers of green plants and seaweed, ki-not top flippers of flagellar protozoa (tripanosomid) and other organoids of cytoplasm. At bacteria and nek-ry lowest eukaryotes conditionally carry to the same successive structural elements episomes (see) and plasmids (see). At last, parasites (endosibionta) living in cells of eukaryotes also can be conditionally carried to them.

Parts the Kappa — a kind of the bacteria which lost ability to independent life and lodged in a body of parameciums where they emit the special toxin killing the individuals deprived of these particles can be the first studied examples of such cohabitation. Other such endosymbiont — the Sigma virus telling fruit flies abnormal sensitivity to carbon dioxide gas is found in a drosophila. These signs are transferred to posterity only if cytoplasm of a zygote is received from the infected parent.

N.'s phenomenon of c. it is described by Korrens (To. Correns) and Baur (E. Yours) in 1908. They established that at flowering plants inheritance of a sign of variegation and transfer of plastids («plastid heredity») is carried out by hl. obr. or even completely through female reproductive cells, i.e. goes on one-parent, but not according to the Mendelian scheme. Afterwards the similar phenomena were found in other higher plants, seaweed, mushrooms, protozoa, insects, in metazoans, including and in the highest mammals and the person.

The cytoplasmatic nature of heredity is proved in various ways, most often — methods of reciprocal and repeated backcrossings (see. Crossing ). Repeated repetition of crossings of type A ♀ x B ♂ x B ♂ ♂ eventually will lead x B to the fact that maternal kernels of a look And at hybrids will be completely replaced with fatherly kernels of a look In, and cytoplasm of a look And will remain. The distinctions found in posterity from these crossings, undoubtedly will indicate the cytoplasmatic nature of inheritance. This method allows to distinguish true plasmatic inheritance from a so-called maternal effect, to-ry on a nek-eye reminds manifestations genetic effect of cytoplasm, but actually is explained pre-determinatspy cytoplasm of an ovum by a genotype of a maternal organism before fertilization.

The following can serve as the proof that cytoplasmatic structures, plasmogenes, define development of nek-ry signs of an organism: detection of the various mutations which are transmitted only through cytoplasm; opening as a part of subcellular organellas of specific DNA, ribosomal, transport and template-RNA and the special device of synthesis of protein; establishment of a direct connection between loss or change of the polidzoksiribonukleotidny sequences in molecule DNA of organellas and change of a phenotype at cytoplasmatic mutants; detection of transmission, segregation and recombination of plasmogenes.

The mutations which are changing or completely breaking functions and characteristic properties of mitochondrions (transport of electrons in a respiratory chain, oktselitelny phosphorylation, sensitivity to a nek-eye to poisons, etc.), were allocated at mushrooms, protozoa and at metazoans. The mutants steady against antibacterial antibiotics, at the lowest eukaryotes and in cultures of cells of mammals are of special interest. Existence of such mutants indicates that the reaction norm of cells consists in sensitivity to these agents and that toxicity of antibiotics for the person is explained by damage of mitochondrions. Set of mutations. changing private reactions in a metabolism and biosynthetic activity of mitochondrions, gives the chance to dismember their functions on separate stages and in such way to approach the analysis of these functions.

The genetic analysis allowed to reveal at Saccharomyces cerevisiae yeast a segregation and rekokhmbina-tssho mitochondrial genes. It made possible establishment of the main features of behavior of the mitochondrial genes distinguishing them from behavior of nuclear genes: existence of a segregation in the course mitosis (see); lack of a segregation at meiosis (see) and polarity of recombinations, i.e. preferential transfer to posterity of a genotype of mitochondrions of one of parents (sexual distinctions at mitochondrions). On the basis of the analysis deletions (see) and point mutations of mitochondrions of yeast cells mapping of considerable number of loci of a mitochondrial genome was made.

Mitochondrions are not formed by de novo, and breed by cell fission. The recombination of mitochondrial genes, at least at yeast, becomes possible thanks to «merge» of mitochondrions, dissociation of their membranes and hereditary contact between molecules of mitochondrial DNA.

The researches executed on the highest animals have special value (including and for the person). So, the segregation and a recombination of mitochondrial genes are established in culture of hybrid somatic cells of «people mouse». Mapping of the genes defining ribosomal and acceptor RNA in culture of cells of HeLa and Xenopus laevis using molecular hybridization of RNA — DNA, a submicroscopy and restriction analysis is made. At mammals intraspecific heterogeneity of mitochondrial DNA is shown and it is established that specificity of this DNA is transferred in generations not through kernels of sex cells, and through cytoplasm.

Results of researches of genetic functions of cytoplasm did not shake the philosophy of genetics, the vast majority of genetic information is born by the chromosomal genes of a cellular kernel concluded in nuclear DNA (see. Deoxyribonucleic acid ). These researches only showed that a part of genetic information contains in DNA of cytoplasm, including in mitochondrial DNA (MTDNK); MTDNK it is presented by the ring covalent closed molecules from 5 microns long at the highest animals to 25 microns at yeast. Molecules MTDNK are formed only from MTDNK, precisely copying the sequence of their polidezoksiribonukleo-tid, and do not duplicate the sequence of nucleotides of nuclear DNA. Gibridizatsionny researches show lack of a homology between MTDNK and nuclear DNA.

The size of molecules of mitochondrial DNA is small, and the genome of mitochondrions cannot provide process of reproduction of structure of mitochondrions completely. Pier. the weight (weight) of mitochondrial DNA fluctuates from 107 at animals to 5 * 10 7 at yeast. The coding capacity of mitochondrial DNA defines structure only of 8 — 15% of structural components of mitochondrions. Big and small ribosomal RNA, about twenty acceptor RNA and 8 — 12 template-RNA belong to their number. Mitochondrial template-RNA, in turn, code a number of components of inner membranes: three subunits of cytochrome oxydase (KF 1.9.3.1) from seven, one subunit of cytochrome b from two, four subunits ATF-sintetazy (KF 3.6.1.3) from ten and still neidentifi-tsirovanny products, components apprx. only 40% of the coding capacity mitokhon; tlny DNA. Also the substances controlling growth and other functions of a cell as whole (ekstramitokhondri-alny functions of mitochondrions) are among such nepdentifitsirovanny products. Products of a mitochondrial genome are synthesized by mitochondrial ribosomes (see), reminding bacterial ribosomes on a number of properties. However the prevailing part of polypeptides of integral components of mitochondrions is coded by chromosomal genes and synthesized in ribosomes of cytoplasm. These nuclear tsitoplazkhmaticheskiye products are delivered in a mitochondrion and here connect with polypeptides and, synthesized in mitochondrial ribosomes therefore uniform oligomerous fermental complexes are formed. Dependence of mitochondrions on a kernel is not limited to it. Other important factor is control of a kernel over processes of replication, a recombination, transcription and broadcast of mitochondrial DNA. Control of a kernel is that the enzymes participating in these processes are products of nuclear genes. All this demonstrates that genetic functions of mitochondrions are only partly carried out independently, in that measure in what it is defined by specificity of mitochondrial DNA. But also mitochondrions, in turn, make a nek-ry contribution to functions of nucleocytoplasmic system.

The mitochondrial mutations breaking nuclear system at yeast and parameciums testify to it. Thus, the kernel and mitochondrions form the integrated genetic system of a cell, and a contribution of mitochondrions though relatively and it is very small, but is unique and cannot be compensated by activity of a kernel.

The genetic system of chlorolayers defining functions of transformation of solar energy to energy of chemical reactions in a green earth's mantle in principle is organized like mitochondrial system. Double genetic control over functions of a cell with participation of a kernel and cytoplasm provides reliability and accuracy of regulation of processes of energy conversion in the organic world.

See also Variability , Inheritance , Heredity .



Bibliography: To Gauza G. G. Mitochondrial DNA, M., 1978; Genetic functions of organoids of cytoplasm, under the editorship of S. A. Neyfakh, D., 1974; Kallinikova V. D. Cellular organellas and ki-not top flippers, L., 1977; Molecular genetics of mitochondrions, under the editorship of S. A. Neyfakh and A.S. Troshin, JI., 1977; Beale G. and. Knowles J. Extranuclear genetics, L., 1978; In og st P. Grivell L. A. The mitochondrial genome of yeast, Cell, v. 15, p. 705, 1978; The genetic function of mitochondrial DNA, ed. by G. Saccone a. A. M. Kroon, p. 15, Amsterdam, 1976; Whitehouse H. L. K. Towards an understanding of the mechanism of heredity, L., 1969.


S. A. Neyfakh.

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