biologists believe that adaptation occurs through the accumulation of small changes, such as the slight differences between parents and their children, some of which can result from mutations. However, an alternative that has been suggested for this process is macromutation, essentially when a sudden large-scale mutation produces a characteristic. This theory has generally been disregarded as the major explanation for adaptation, since a mutation on this scale is regarded as more likely to be detrimental than beneficial.
While macromutations appear to be the only explanation for differences such as the number of body segments among
arthropods, at the genetic level where the original change occurs, very few changes to genes may actually be necessary to result in the large physical change. Some genes control other genes and the higher the level of control, the larger the change it can make (see Homeobox). Biologists make a distinction between changes to the genotype, and the resulting body structure resulting from those genes phenotype.
polydactylyindividuals have a large resulting change in their body structure (extra toes), but can result from a small change in their genotype. This is not the only possible cause of such changes. They can also result from errors during development, but such non-gene changes are not inherited by future generations.
Macromutation in Chromosomes
Instantaneous biological adaptation must occur when a non deleterious or rarely useful change occurs in the number of chromosomes in the organism's
phenome. This must have occurred when the ancestral ape produced offspring which possessed 46 instead of 48 chromosomes, leading to the eventual evolutionof humanity.
This change cannot have taken place slowly as odd numbers and partial chromosomes in diploid creatures are not reproductively viable. Although the possibility of finding a similarly endowed mate to enable reproduction is rather unlikely, the evolution from a single-celled organism to the complex multi-cellular beings found today was equally unlikely, making the possibility not entirely impossible and a rather viable rationale for the differences in chromosome number between the other Great Apes and humans.
This does not invalidate adaptation taking place as a result of slowly developing variation acted on by
natural selection, as the genetic sequencing changes wrought by natural selection may lead to chemical instability of the genome concerned causing fusion, splitting of chromosomes, usually deleterious, but very occasionally useful.
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macromutation — macromutation. См. комплексная мутация. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) … Молекулярная биология и генетика. Толковый словарь.
macromutation — ● macromutation nom féminin Mutation affectant de larges portions d un chromosome, responsable de certaines aberrations chromosomiques. (Par opposition à micromutation.) … Encyclopédie Universelle
macromutation — didžioji mutacija statusas T sritis augalininkystė apibrėžtis Mutacija, kurios metu labai pakinta genetinė medžiaga ir organizmo požymių išraiška. atitikmenys: angl. large scale mutation; macromutation rus. крупная мутация; макромутация ryšiai:… … Žemės ūkio augalų selekcijos ir sėklininkystės terminų žodynas
macromutation — n. [Gr. makros, large; mutare, to change] Theory of instantaneous evolution of new taxa by a mutation that establishes reproductive isolation at once … Dictionary of invertebrate zoology
macromutation — /mak roh myooh tay sheuhn/, n. Genetics. a mutation that has a profound effect on the resulting organism, as a change in a regulatory gene that controls the expression of many structural genes. [MACRO + MUTATION] * * * … Universalium
macromutation — mac·ro·mu·ta·tion myü tā shən n complex mutation involving concurrent alteration of numerous characters … Medical dictionary
macromutation — mac·ro·mutation … English syllables
macromutation — mac•ro•mu•ta•tion [[t]ˌmæk roʊ myuˈteɪ ʃən[/t]] n. gen a mutation that results in a profound change in an organism, as a change in a regulatory gene that controls the expression of many structural genes … From formal English to slang
macromutation — … Useful english dictionary
комплексная мутация — macromutation, complex mutation макромутация, комплексная мутация. Крупное изменение генетического материала (мутации структурных генов, изменения количества избыточной ДНК, хромосомные перестройки и др.), лежащие в основе импульсной… … Молекулярная биология и генетика. Толковый словарь.