thường biến

From Wikipedia, the không tính phí encyclopedia

Bạn đang xem: thường biến

Ecophenotypic variation ("ecophenotype") refers to lớn phenotypical variation as a function of life station. In wide-ranging species, the contributions of heredity and environment are not always certain, but their interplay can sometimes be determined by experiment.


Plants display the most obvious examples of ecophenotypic variation. One example are trees growing in the woods developing long straight trunks, with branching crowns high in the canopy, while the same species growing alone in the open develops a spreading size, branching much lower to lớn the ground. Genotypes often have much flexibility in the modification and expression of phenotypes; in many organisms these phenotypes are very different under varying environmental conditions. The plant Hieracium umbellatum is found growing in two different habitats in Sweden. One habitat is rocky sea-side cliffs, where the plants are bushy with broad leaves and expanded inflorescences; the other is among sand dunes where the plants grow prostrate with narrow leaves and compact inflorescences. These habitats alternate along the coast of Sweden and the habitat that the seeds of H. umbellatum land in determines the phenotype that grows.[1] Invasive plants such as the honeysuckle can thrive by altering their morphology in response to lớn changes in the environment,[2] which gives them a competitive advantage. Another example of a plants phenotypic reaction and adaptation with its environment is how Thlaspi caerulescens can absorb the metals in the soil to lớn use to lớn its advantage in defending against harmful microbes and bacteria in its leaves.[3] The more immediate responses shown by vascular plants to lớn their environment, for instance a vine's ability to lớn conform to lớn the wall or tree upon which it grows, are not usually considered ecophenotypic, even though the mechanisms may be related.[4]


Xem thêm: dàn ý vợ chồng a phủ

Since animals are far less plastic than vãn plants, ecophenotypic variation is noteworthy. When encountered, it can cause confusion in identification if it is not anticipated. The most obvious examples are again common observations, as the dwarfing of aquarium fish living in a restricted environment.[5] In asexual reproduction, the parent passes on the entire genome to lớn the next generation. Mutations to lớn the genes are the only source of genetic variation. In sexual reproduction, each parent contributes half of his or her genome to lớn the offspring; thus the offspring contain a mixture of genetic material. Adaptations are traits that increase fitness, the driving force for natural selection. The level of fitness associated with an allele can only be ascertained by comparison with alternate alleles. Traits that increase the survival rate of a species contribute to lớn an animal's fitness, but selection will only favor such traits insofar as survival improves the reproductive success of the organism. More interesting are examples where causation is less clear. Among mollusks, examples include the muricid snail species Nucella lamellosa, which in rough, shallow waters is generally less spiny than vãn in deeper, quiet waters.[6] In unionid freshwater bivalves, there are lake, small river, and large river forms of several species.[7] In vertebrates, experiments on mice show reduced length of ears and tails in response to lớn being reared in a lower temperature, a phenomenon known as Allen's rule.[8]


In humans, environmental differences due to lớn lifestyle choices are a consideration, for instance the differences between someone who spends much time on the sofa before the television, beer in hand, and an individual who spends his time in the thể hình or the soccer field can be pronounced. Franz Boas found that cephalic index was to lớn some degree dependent on where a child was born, independent of the child's genetic or cultural heritage.[9] Another way in which environmental differences can cause physical and/or behavioral alterations is in being put under great levels of stress, causing a wide range of effects. Chronic Stress has been proven to lớn cause health issues in many individuals. "Early childhood attempts to lớn cope with fear or rejection ... phối up psychological patterns of behavior for the person's later life. Those behaviors in turn affect the biochemical imbalances in the brain's neuronal systems. Those altered imbalances in turn reinforce the behaviors, and the cycle feeds upon itself." "The body toàn thân reacts biochemically to lớn excessive stress as it attempts to lớn regain its healthy dynamic balance" ; "In psychologically stressful situations, hormones may be brought into play to lớn remedy the imbalance the body toàn thân finds itself in."[10]

In the General Adaption Syndrome, which is the biological response to lớn stress, there are three stages. 1.) The "Alarm Action" - heart rate increases, blood sugar levels rise, pupils dilate, and digestion slows. 2.) The "Resistance" or "Adaptive" stage - The body toàn thân attempts to lớn repair the damage which caused the emergency arousal 3.) The "Exhaustion Stage" - The body toàn thân grows ill; Mentally, possibly by neurosis or even psychotic disturbances, or physically, having the possibility to lớn trigger several kinds of cardiovascular and kidney diseases, and Quite commonly, certain forms of asthma.[10]

Xem thêm: nền nếp hay nề nếp


  1. ^ "Botany online: Evolution: The Modern Synthesis - Phenotypic and Genetic Variation; Ecotypes". Archived from the original on 2009-06-18. Retrieved 2009-12-29.
  2. ^ Schweitzer, Jennifer; Larson, Katherine (1999). "Greater morphological plasticity of exotic honeysuckle species may make them better invaders than vãn native species". Journal of the Torrey Botanical Society. 1 (126): 15–23. doi:10.2307/2997251. JSTOR 2997251.
  3. ^ "Plants 'armor up' with metals." Science Online. Facts On File, Inc. Web. Retrieved 10 May 2013.
  4. ^ Gibson, J. Phil, and Terri R. Gibson. "plants and the environment." Science Online. Facts On File, Inc. Web. Retrieved 10 May 2013.
  5. ^ Cullen, Katherine. "evolution." Science Online. Facts On File, Inc. Web. Retrieved 10 May 2013.
  6. ^ Abbott, R. T., 1968 Seashells of North America. Golden Press, Thủ đô New York.
  7. ^ Burch, J. B., 1975 Freshwater unionacean clams (mollusca, Pelecypoda) of North America. Malacological Publications. p 39.
  8. ^ Ashworth, William, and Charles E. Little. "Allen's rule." Science Online. Facts On File, Inc. Web. Retrieved 10 May 2013.
  9. ^ Rice, Stanley A. "environmental psychology." Science Online. Facts On File, Inc. Web. Retrieved 10 May 2013.
  10. ^ a b Davis, J. (1984) Endorphins. Garden City, N.Y.: Dial Press.