modification

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modification

[‚mäd·ə·fə′kā·shən]
(cell and molecular biology)
In nucleic acid metabolism, any changes made to deoxyribonucleic acid or ribonucleic acid after their original incorporation into a polynucleotide chain.
(engineering)
A major or minor change in the design of an item, effected in order to correct a deficiency, to facilitate production, or to improve operational effectiveness.
(metallurgy)
Treatment of molten aluminum alloys containing 8-13% silicon with small amounts of a sodium fluoride or sodium chloride mixture; improves mechanical properties.
(science and technology)
Any change brought about by external or internal factors.

Modification

 

in biology, nonhereditary changes in the visible characters (phenotype) of an organism; these changes occur under the influence of altered environmental conditions.

Modifying factors in the environment (temperature, illumination, diet) act on the organism during sensitive periods of its development, precipitating changes in the organism’s internal makeup (for example, changes in hormone level) and altering the course of ontogeny. Modificational variation consists in changes within the limits of the genotypically conditioned norm of reaction. Depending on the temperature of its environment, the Himalayan rabbit may change from black in cold weather to rusty brown in mild temperatures to pure white in high temperatures. However, the coloration of the parent rabbits is not inherited by their young; only the capacity to change color according to temperature change is inherited.

In nature, modifications are, as a rule, adaptive reactions of organisms to environmental factors. Thus, in lake Sagittaria sagittifolia, the shape of the leaves depends on where they grow: the above-water leaves are arrow-shaped, the leaves that float are heart-shaped with stomata on the upper side, and the underwater leaves are ribbon-like. Nonadaptive modifications often consist of all kinds of developmental disturbances, the extreme expression of which includes deformities and morphological and physiological malfunctions. These modifications occur, as a rule, in response to strong external stimuli, to which individuals of a given species are rarely exposed under normal conditions.

In contrast to mutations, modifications are not transmitted by heredity. Modifications develop in individuals of a given generation only when the conditions under which these modifications normally arise are present. However, in unicellular and occasionally multicellular organisms, prolonged modifications are found when changes in visible characters that have arisen as a result of environmental factors are retained for several generations, even after the disappearance of the inducing factors. This type of modification is apparently caused by changes in relatively stable self-reproducing cytoplasmic structures. Since they are nonhereditary, modifications have no direct evolutionary significance. If, however, a phenotype formed as a result of modification has a high adaptive value, the phenotype may become fixed in evolution only through the selection of those mutants that retain a given modification, but discard other modifications of a given character.

REFERENCES

Lobashev, M. E. Genetika, 2nd ed. Leningrad, 1967.
Shmal’gauzen, I. I. Faktory evoliutsii. Moscow, 1968.

N. V. TIMOFEEV-RESOVSKII, V. I. IVANOV and V. A. MGLINETS

modification

1. A written amendment to the contract document signed by both parties.
3. A written or graphic interpretation issued by the architect.
4. A written order for a minor change in the work, 1 issued by the architect.

modification

An alteration or change meant to rectify faults or shortcomings or which offers improved capability. A modification involves changes in the design of equipment or components.
References in periodicals archive ?
N6-methyladenosine RNA modification regulates embryonic neural stem cell self-renewal through histone modifications," Nature Neuroscience 2018; DOI: 10.
De Crecy-Lagard had previously discovered many of the genes required for the synthesis of RNA modifications known as queuosine and archeosine, which are found in microorganisms and are derived from a common precursor called preQ0.
8] introduce modeling method of spur bevel gear and then confirm the amount of tooth profile modification according to the analysis of simulation results; Barone et al.
He said: "Speeding is the most attractive part of modifications for youngsters.
Yet, many lenders argue that not all homeowners are properly taking the steps they must to qualify for a home loan modification and, simply put, not every homeowner will meet the demands of the Home Affordable Modification Program and get a home loan modification.
The best indicator of whether a company will renew a contract or do so without material modification is the company's history of renewals/extensions of this or similar contracts.
The researchers can then wrap these designer histones with DNA and examine how combinations of histone-tail modifications influence a gene's activity.
Part I of this two-part article discusses the purchase of software subject to the first two rules, as well as software modification costs and the current deduction for leased software.
However, this task can be accomplished by providing adaptations, accommodations, and program modifications to the general education curriculum, along with supports to the general education teacher, to assist the student in acquiring mastery of required content.
There is money for accessibility modifications out there.
Designed as a guide to understanding the needs and latest trends in organizing the living space of elderly people, this book provides access to several studies on elderly people's environmental needs and preferences in regard to modifications in personal and public dwellings.

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