Extranuclear inheritance

The majority of DNA, and therefore genetic information, is stored in the nucleus of eukaryotic cells . The set of genes whose DNA is located in the cytoplasm is called the plasmosome . However, a small part (about 2%) is located outside the nucleus, in some organelles:

• mitochondria
• chloroplast

They can arise independently of the reproductive cycle of the cell, but cannot arise de novo . The laws of inheritance conditioned by plasmids do not agree with Mendelian rules (so-called non-Mendelian inheritance ).

Manifestations of extranuclear inheritance

The results of reciprocal crossing are not identical , extranuclear traits cannot be studied in connection with nuclear inheritance. The offspring of individuals hybrid for extranuclear genes split in proportions that cannot be interpreted in accordance with knowledge of the splitting, combinability and interaction of genes located on nuclear chromosomes .

Evidence of extranuclear inheritance

In some cases, the phenotype is not demonstrably controlled by nuclear genes. Experimental nuclear replacement in cells clearly demonstrates the proportion of nuclear and extranuclear inheritance. Transmission of traits without nuclear transfer indicates extranuclear inheritance. Extranuclearly controlled traits more often show autosomal cleavage.

Plastid-linked inheritance

Plastids are organelles typical of plant cells. They are separated from the cytoplasm by a semipermeable membrane. They arise by self-reproduction, division, or from proplastids.

Mitochondrial inheritance

Mitochondrial DNA For more detailed information, see the Mitochondrial Inheritance page .

Mitochondrial inheritance is encoded on mtDNA (mitochondrial DNA) . It is very similar to prokaryotic DNA (circular chromosome, without introns,…). It is located in the matrix of mitochondria. It does not have repair systems. Mitochondrial diseases are chronic and often with late onset .

Matrilineal inheritance

Mitochondrial DNA is inherited exclusively from the mother , because during fertilization of the egg, the paternal mitochondria from the sperm are destroyed (damaged by the high power that the sperm needs to move). In exceptional cases, both maternal and paternal mitochondria can be found in the cytoplasm of an individual (they were not destroyed in the zygote). Such an individual is called a cybrid (cytoplasmic hybrid, chimera).

The genes contained in the mtDNA molecule encode respiratory chain proteins , ATPase complex units, NADH -dehydrogenase complex subunits, two ribosomal RNAase genes, and 22 transfer RNA molecules . Mitochondria-bound genes, are inherited by so-called cytoplasmic inheritance .

Hereditary mitochondrial diseases

For more detailed information, see the Mitochondrial Diseases page .

The molecular genetic basis of mitochondrial pathologies can be either deletions of a 5 kb region between the genes for ND5 (NADH-dehydrogenase subunit 5) and ATPase 8 (ATPase subunit 8) or point mutations (mostly changing the reading sense of the codon - missense or substitution).

• Kearns-Sayre syndrome — progressive external ophthalmoplegia , retinal pigment degeneration, cardiac and cerebellar problems.
• Mitochondrial pathology caused by point mutations:
  • LHON ( Leber's Hereditary Optic Neuropathy ) — blindness in males under 25 years of age; penetrance of the disease is 3-4 times higher in males than in females.
  • MELAS (Mitochondria Myopathy, Encephalopathy, Lactic Acidosis, Stroke-like episodes) — first symptoms appear between the 5th and 15th year of an individual's life, single nucleotide substitution in the gene for leucine tRNA (position 3243).
  • MERF (Myoclonic Epilepsy with Ragged red Fibers) — manifestation between the 5th and 12th years of an individual's life.

Links

Related articles

• Matrilineal inheritance
• Mitochondrial inheritance
• Mitochondrial disease
• Mitochondria

Source

• ŠTEFÁNEK, Jiří.  Medicine, diseases, study at the 1st Faculty of Medicine, Charles University  [online]. [cited 11. 2. 2010]. < https://www.stefajir.cz/ >.