Genome mutation

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A genome mutation is a change in the number of chromosomes in an organism or cell . Such changes in a cell are passed on to the daughter cells. Arise from these cells daughter organisms (animals ie in cells of the germ line ), the genome mutation to offspring inherited .

Genome mutations are combined with chromosome mutations , in which the structure of the chromosomes visible under the light microscope, to form chromosome aberrations : Chromosome mutations are referred to as structural chromosome aberrations, genome mutations as numerical. In contrast, mutations that only affect a single gene and are therefore not visible with a light microscope are referred to as gene mutations .

Types of Genome Mutation

Polyploidy

In polyploidy , all chromosomes of a chromosome set are not duplicated (diploid), but multiple (i.e. at least triply / triploid). Often it is caused by the lack of a spindle apparatus .

Economic usability

Polyploidy often occurs in crops . On the one hand this can be a mistake or a coincidence, on the other hand (and much more often) it is a deliberate increase in chromosomes caused by humans . Thanks to genetic engineering , crops (especially wheat ) are now even grown as hexaploids (6 genome sets) or even octaploids (8 genome sets) due to their higher yield. The higher yield of the genetically modified crops can be explained by the resulting enlargement of the cell. The increase can be explained by the fact that each genome codes for its own task. Since the genome in octaploidy is now available 8 times, the respective task is also carried out 8 times.

Situation in humans

This form of genome mutation can also occur in humans, but the lethality of the embryos is 100%. Such a genome mutation can in no way be survived by humans. The human organism can only survive the change or multiplication of a single chromosome ; however, some of the most severe disabilities occur here (see aneuploidy).

Aneuploidy

Aneuploidy is always a flawed process. The multiplication of just one chromosome does not result in any desirable change. The addition of individual chromosomes always leads to a malformation.

In aneuploidy , the number of individual chromosomes is increased or decreased, which is attributed to irregularities during cell division. The cause is usually a faulty separation of the chromosomes during cell division ( non-disjunction ). The best- known example is Down's syndrome in humans.


In humans

In contrast to polyploidy (see above), adding individual chromosomes (a so-called trisomy ) does not necessarily lead to a miscarriage . Whether or not a miscarriage occurs, as well as the type of physical change, depends on the chromosome affected. However, massive physical and mental disabilities are to be expected in some cases (depending on the location of the trisomy) .

The following chromosomes can be completely affected without an immediate abortion:

With all three of the trisomies mentioned, the most severe disabilities of the internal organs and the brain occur (as a rule). The affected infants usually have a pronounced developmental delay on both a physical and a mental level. People with trisomy 13 and 18 rarely reach the age of 10 years. In contrast to trisomy 21 (which is mainly characterized by intellectual disability), the entry into adulthood has never been observed (has never been recorded) with these forms of trisomy. Despite the massive medical progress, due to the massive organ damage associated with trisomy 13 and 18, a later entry of these infants into adulthood in the next few years is as good as impossible.

If the sex chromosomes (gonosomes) are affected by the trisomy, the consequences for those affected are usually less dramatic. Such severe disabilities as occur, for example, in trisomy 21, have not yet been observed in gonosomal trisomy. Often a restricted fertility (fertility) occurs (sometimes leading to infertility (sterility) ). However, the possibility of building an erection and having sexual intercourse is not restricted. In some cases (especially in Jacobs syndrome "super man syndrome") there is even an increased sex drive (libido) . Behaviors that are typical of men (for example, increased willingness to be aggressive) are also due to the pathologically increased testosterone level . The following gonosome trisomies can occur:

The comparatively minor effects of a gonosome trisomy can be explained by the specific size of the chromosome. The larger a chromosome, the larger parts of the organism it encodes. The sex chromosomes are the smallest chromosomes found in the human genome and therefore only encode very small areas of the human gene code.

The following chromosomes are viable if the chromosome is only partially (partially) hit . If the complete chromosome is hit, the fruit cannot survive.

If another chromosome is hit, it inevitably leads to a miscarriage, as the embryo is not viable.

See also

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  1. ↑ William Hovanitz: Textbook of Genetics. Elsevier Press, Inc., Houston, New York, 1953 (p. 190). "(...) if a change in structure (of chromosomes) is large enough to be visible in cytological preparations it is considered a chromosomal mutation. If it is too small to be readily observed, is known only from the genetic results of segregation and can be localized on a chromosome, it is known as a gene mutation. There is no sharp dividing line between gene mutations and chromosomal mutations. Eventually all gene mutations in their ultra-fine structure will be found to be structural, if only in the molecular arrangement of which the gene is composed. "
  2. ↑ Werner Buselmaier, Gholamali Tariverdian: Humangenetik. Text accompanying the item catalog. Springer Verlag Berlin Heidelberg New York, 1991, ISBN 3-540-54095-4