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
Oxygen Dissociation Curves The oxygen content of blood fully saturated or oxygenated can be calculated. It is known as the oxygen capacity of blood and this varies for differe


1. Andalusian chickens may be either black, white, or gray. The gene for black is not dominant over the gene for white, nor is the gene for white dominant over the gene for black.

What is Human Glucose Transporters (GLUT)? All GLUTS are the integral proteins, which penetrate and span the lipid bilayer of plasma membrane. Six isomers of GLUT have been des

Carpentier: Edwards or similar annuloplasty ring is then sutured into place by interrupted sutures to support the repair and reduce the annulus to a measured amount. The ring m

What is Mitochondria ? Mitochondria are the cellular organelles responsible for the conversion of energy into a form called ATP. ATP is a high energy chemical compound that cel

Many disease states are heralded by changes in the blood count Leukocytosis can be a sign of infection. Thrombocytopenia can result from drug toxicity. Pancytopenia is ge

Explain Basal Metabolism Rate (BMR) - Ageing? From age 25 years, the basal metabolism decreases by about 2 percent for each decade due to the increasing proportion of body fat

Define Prevalence of Weight Management? WHO (1998) estimates that in developing countries about 245 million adults are moderately underweight and 93 million severely underweigh

Prostaglandins and the structurally associated molecules prostacyclins, leukotrienes and thromboxanes, are called as eicosanoids because they having 20 carbon atoms. These hormones