Action of natural selection in changing environments, Biology

Assignment Help:

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.


Related Discussions:- Action of natural selection in changing environments

Describe the stages of atherosclerosis, Describe the Stages of Atherosclero...

Describe the Stages of Atherosclerosis ? The process of atherosclerosis which gives rise to CAD marches in stages. The earliest recognizable pathologic lesions are the fatty st

What are biogeochemical cycles, Q. What are biogeochemical cycles? The ...

Q. What are biogeochemical cycles? The Biogeochemical cycles are representations of the circulation and recycling of matter in nature. The major biogeochemical cycles studie

PHYUM, HOW MANY PHYLUM OF ANIMALS?

HOW MANY PHYLUM OF ANIMALS?

What is the type of reproduction that occurs in roundworms, What is the typ...

What is the type of reproduction that occurs in roundworms? What typical element do nematode sperm cells have? Nematodes reproduce sexually. The nematode sperm cell does not h

Synthetic petrol, Petrol or gasoline can be synthesized by following three ...

Petrol or gasoline can be synthesized by following three methods: 1.      Polymerisation 2.      Fischer - tropsch method 3.      Bergius process polymerisation In

Agro industrial-evaluation of feedstuff, Evaluation of feedstuff In th...

Evaluation of feedstuff In the feed manufacturing process evaluation of the feed ingredients is very important in achieving consistent quality throughout the year. If one is a

Mechanism of blood coagulation, GENERA L MECHANISM OF BLOOD COAGULATION - ...

GENERA L MECHANISM OF BLOOD COAGULATION - All researchers agree that blood clotting is a cascade mechanism and involves three essential steps - (a) Formation of prothrombin ac

Impulse transmission, The conduction of impulse in a nerve fibre is. a elec...

The conduction of impulse in a nerve fibre is. a electrochemical process. Maximum speed of transmission of nerve impulse can be 13 metre/second due to axoplasm is much resistant to

What is the difference between taeniasis and cysticercosis, Q. What is the ...

Q. What is the difference between taeniasis and cysticercosis? The Taeniasis is the parasitic disease caused by the adult tapeworm installed within the human intestine. The

Is the ventricle lumen larger during systole, Is the ventricle lumen larger...

Is the ventricle lumen larger during systole or during diastole? Systole is the stage of the cardiac cycle on which the ventricles contract. So the lumen of these chambers is d

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd