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
Annuloplasty with a Ring :  The lings commonly used are Carpentier- Edwards and Cosgrove's flexible half ring. The rings are C shaped and have incomplete circles to accommoda

Define Changing Trends in Dietary Intake? As a practicing dietician, you must be sensitive to the society as a whole. The fat requirements have been worked out with a premise o

Mention the role o ribosome's in peptide -bond formation .How does ATP facilitate it? a) Of springs derived by asexual reproduction are known as clones. Justify giving two R

Ascariasis This disease is found in young calves causing digestive disturbances and poor growth. E t iology: It is caused by Toxocara vitulorum in cow and buffal

If NAD+ is an electron acceptor that becomes NADH and the NADH then donates a proton to ATPase, shouldn't NADH now become NAD- since it lost it's proton but still has the electron?

Agroup of realated genera are classified as-?

Precipitation/Solubility of Proteins Most of the functional properties are  dependent on the degree to which the proteins are soluble. The solubility behaviour provides a good

Posterior Leaflet: In the posterior leaflet a quadrangular excision of the sector involved in the prolapse is done. This may be up to 15-20 per cent of the leaflet. The remaining

Explain Sickle cell anemia If 4% of a people are born with a severe form of sickle cell anemia. what percent of population will be resistant to malaria in spite of carrying

Question 1: (a) Give, in order, the major categories of taxonomic classification. (b) Differentiate between the five kingdoms of organisms. (c) Differentiate between net