Action of natural selection in changing environments, Biology

Directional or progressive selection is the mode of selection associated with environmental change. We said earlier that in an unchanging environment stabilising selection removes "unusual" forms of traits or extreme measurements every generation. But in an altered environment, the previous mean may no longer be the optimal measurement of the trait. Under these circumstances, selection would weed out the individuals from the two ends of the normal curve unequally.

This in turn shifts the mean of the trait to a new favoured extreme, You may understand that directional selection is a modified form of stabilising selection in that it does not work evenly.at both ends of the distribution curve. A revealing example of directional selection in operation is the ability of pest populations to develop resistance to pesticides. Man has been largely responsible for changes in the environment of many organisms. In order to adapt thcmsclvcs to changes in environment, organisms respond rapidly through directional selection. Ever since the first report on the resistance of houseflies to DDT was made in 1947, more and more reports of insects becoming resistant to a variety of pesticides have been coming in over the past four decades. In all cases the story.is same: Initially a l small concentration of a new pesticide is sufficient to control thc pests. Slowly the concentration is increased even as the insects develop resistance to higher concentrations. Finally the pesticide becomes totally ineffective or the use of it is economically impractical.

Posted Date: 4/6/2013 1:32:58 AM | Location : United States







Related Discussions:- Action of natural selection in changing environments, Assignment Help, Ask Question on Action of natural selection in changing environments, Get Answer, Expert's Help, Action of natural selection in changing environments Discussions

Write discussion on Action of natural selection in changing environments
Your posts are moderated
Related Questions
how trematodes/nematodes adapt to their parasitic mode of feeding

How are the epithelial tissues classified? The epithelial tissues are classified according to the shape of the cells that form it (epithelial cells may be cuboidal, columnar, o

Respiratory Protection - Azotobacter In respiratory protection N 2 -fixing cells adjust the rate of .aerobic respiration according to prevailing oxygen tension i.e. rising and

What is Prostetic group Prostetic group :- A non-protein  part  of  the  enzyme which  remains  tightly bound to the protein part.

Erysipeloid A zoonosis called erysipelas in animals, rose disease in pig, erysipaloid in man is caused by Erysipelothrix rhusiopathiae (insidiosa). Other names given to this co

Q. What is the cell theory? Cell theory asserts that the cell is the element unit of living beings. Before the discovery of the cell, it was not acknowledged that living bei

Define Methods of Quantitative Analysis and Colorimetry? Many methods of quantitative analysis are based upon the production of coloured solutions in such a way that the intens

Diagnosis X-ray chest shows cardiomegaly.  ECG shows conduction defect, low voltage QRS, atrial and ventricular disrhythrnias.  Echocardiogram - decreased LV cont

What is the plasma membrane of the cell? What are its main functions? The plasma membrane is the outer membrane of the cell; it delimits the cell itself and a cell interior wit

Explain Class adverse effects of Protease inhibitors   Many protease inhibitors can cause gastrointestinal distress, increased bleeding in hemophiliacs, hyperglycemia, insulin r