Tuesday, March 31, 2009

Adaptation the special feature of Organisms

The existence of an organism in its environment or habitat is closely related to the special features of that organism or the adaptations. Adaptation is the special feature of an organism's morphology, anatomy, and physiology, which improves its interaction with its environment.

Adaptations usually have the following characteristics.
1) Special features are specially suited to a specific habitat.
2) These special features are often complex.
3) These special features help organisms to live in their environment and capture food, regulate the body's physiology, reproduce, disperse, and defend against enemies.

Adaptation is one of the important factors that drives the process of evolution. Adaptations are created through mutation and natural selection. Evolution requires genetic variation. In order for continuing evolution there must be mechanisms to increase or create genetic variation and mechanisms to decrease it. Mutation is a change in a gene. These changes are the source of new genetic variation. Natural selection operates on this variation. If these variations are suited to the changed environment that organism will outperform the others, which leads to the evolution of the population. If these new changes created through mutation are not suitable for existence in that environment, they will lead to extinction.Natural selection:Some types of organisms within a population leave more offspring than other Over time, the frequency of the more prolific type will increase. The difference ii reproductive capability is called natural selection. Natural selection is the only mechanism of adaptive evolution; it is defined as differential reproductive success of pre-existing classes of genetic variants in the gene pool.

The most common action of natural selection is to remove unfit variants as they arise via mutation. In other words, natural selection usually prevents new alleles from increasing in frequency. This led a famous evolutionist, George Williams, to say "Evolution proceeds in spite of natural selection."

Natural selection can maintain or deplete genetic variation depending on how it acts. When selection acts to weed out deleterious alleles, or causes an allele to sweep to fixation, it depletes genetic variation. When heterozygotes are more fit than either of the homozygotes, however, selection causes genetic variation to be maintained. (A heterozygote is an organism that has two different alleles at a locus; a homozygote is an organism that has two identical alleles at a locus.) This is called balancing selection. An example of this is the maintenance of sickle cell alleles in human populations subject to malaria. Variation at a single locus determines whether red blood cells are shaped normally or sickled. If a human has two alleles for sickle cell, he /she develops anemia-the shape of sickle cells precludes them from carrying normal levels of oxygen. However, heterozygotes who have one copy of the sickle cell allele coupled with one normal allele enjoy some resistance to malaria--the shape of sickle cells make it harder for the plasmodia (malariacausing agents) to enter the cell.

Thus, individual homozygous for the normal allele suffer more malaria than heterozygotes. Individual homozygous for the sickle cell are anemic. Heterozygotes have the highest fitness of these three types. Heterozygotes pass on both sickle cell and normal alleles to the next generation. Thus, neither allele can be eliminated from the gene pool. The sickle cell allele is at its highest frequency in regions of Africa, where malaria is most pervasive. Balancing selection involves opposing selection forces. An equilibrium results when two alleles selected in the homozygous state are retained because of the superiority of heterozygotes. Balancing selection is rare in natural populations.

Tags: Bio Technology, Bio Genetics , Adaptation of organisms

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