DELETION (Latin deletio destruction) — loss of the terminal or intersticial site of a chromosome or chromatid. In the first case D. is connected with one gap in a chromosome, in the second — with two. Some authors the term «deletion» designate only intersticial D., and call terminal D. «shortages» (deficiency), but most often both terms in literature are used as synonyms. Designate a Df symbol with the instruction a number of sequence number of a chromosome and symbols of the genes lost as a result of D. if they are known. Sometimes allocate dot Dm carrying to them D. which size is in mitotic chromosomes below resolving power of a light microscope.
Arise as it is induced (action of radiation and other physical. and chemical factors), and spontaneously also make one of the most widespread types of aberrations of chromosomes (see. Mutation ). Large D. are easily identified at tsitol, the analysis of metaphases or anaphases (see. Mitosis ), especially when in a cell the site lost by a chromosome remains; dot D. can be found in the course genetic analysis (see). Because methods of the full accounting of dot D. do not exist yet, the actual number D. in a cell is always much more considered.
Intersticial D.' action depends on their size and localization. Large intersticial D. surely flax whereas small can be retsessivno lethal or even not to influence of summer viability of an individual at all and to be followed in certain cases by phenotypical effect. So, loss of a dominant allele in a heterozygote leads to manifestation of a recessive character. Dot D. phenotypical are shown as point mutations. There is no doubt that the considerable number of so-called point mutations, especially recessive details, is not true genovariations, but dot.
The large number of cases of hereditary pathology at the person can be connected with D. Odnako the condition of cytogenetics of the person allowed to identify generally only aneuploidies (see. Chromosomal complement ), inversion (see) and translocations.
20 century developed in the 70th methods of the analysis of differentiation of chromosomes on length allow to identify individual chromosomes, and in some cases — their segments. It led to detection among live-born children partial D.' syndromes of a short shoulder of chromosomes 4 and 5, a short or long shoulder of chromosomes 9 and 18, a long limb 13 meet with inborn malformations of a number of chromosomal syndromes which are caused by D. Chashche of others.
See also Cytogenetics .
Bibliography: Dubinin N. P. General genetics, M., 1 976; Fundamentals of cytogenetics of the person, under the editorship of A. A. Prokofieva-Belgovskaya, page 363, M., 1969; Suonson K., Mertz T.i Young of U. Tsitogenetik, the lane with English, M., 1969.
N. V. Luchnik.