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 ?
For more information about Fontaine Modification Vocational Services, call 800.
Eric Selk, executive director of HOPE NOW, said, "While loan modifications continue to fall from their peak levels around 2010, delinquencies and foreclosures are showing [a] corresponding decline.
He added that the majority of modifications revolved around tuning engines for extra horsepower and adding loud exhausts.
Side Chain Functional Polyesters and Polycarbonates via Post-Polymerization Modification
The private-sector group noted that the combination of short sales, total loan modifications, deeds in lieu and workout plans outpaced foreclosure sales by four to one.
Besides the areas of new thermal protection, the modifications included better protection for its radiators against space debris, and touch-screen electronic instruments to replace the 1970s-era video screens and mechanical gauges.
A group of NIEHS scientists has recently perfected a new in vivo gene modification technique that enables researchers to quickly generate site-directed mutations onto specific regions of the yeast genome without leaving behind foreign DNA.
Modifications to the current transfer tax system that are analyzed in the study include:
Despite all my modifications, I found that I simply could not meet the challenge anymore.
modification of the task to alter the existing method of completing a task so that it can be accomplished in an alternative manner; and
Evaluators are responsible for the safety of the client during the evaluation, determining the driving abilities of the client, and in making an appropriate determination of adaptive equipment and vehicle modifications.
Bank of America completed nearly 25,000 mortgage modifications for financially distressed homeowners in October, up from about 16,500 in the previous month.

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