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

What is enteropathogenic escherichia coli, Escherichia coli is generally re...

Escherichia coli is generally regarded as part of the normal flora of the human intestinal tract and that of many animals. Serotypes of E. coli which have been implicated in human

Freeze fracture electron microscopy, Freeze Fracture Electron Microscopy ...

Freeze Fracture Electron Microscopy Freeze fracture electron microscopy i a technique lo reveal the surface features of hydrophobic interior of cell membrane. In this technique,

Define growth and development of infants and preschoolers, Define Growth an...

Define Growth and Development of Infants and Preschoolers? In this unit, we learnt about the various aspects related to the growth and development of infants and preschoolers.

Poultry and duck diseases-avian reovirus infections, Avian reovirus infecti...

Avian reovirus infections There are several avian reoviuses isolated from chicken, turkey and other species of birds. They are associated with arthritis (tenosynovitis), respir

State in brief about the alexander luria, State in brief about the alexande...

State in brief about the alexander Luria Luria adopted or developed these items over the course of many years, Christensen published them in English but without standardisatio

Pneumothorax, Pneumothorax Entry of air in the pleural cavity is calle...

Pneumothorax Entry of air in the pleural cavity is called pneumothorax. It may be spontaneous, result of penetrating or non-penetrating injuries. Closed Pneumothorax

What are his morning and bedtime doses, a) Donald is a 50 year old male wit...

a) Donald is a 50 year old male with a long history of bipolar disorder. He has been hospitalized three times in the last 8 months for manic episodes. He was just admitted to your

What is the significance of axial skeleton, What is the significance of Axi...

What is the significance of Axial skeleton? The bones which make up skeleton of the main body axis of vertebrates. It comprise the cranium, vertebral column, and rib cages, How

Agricultural activities - cause of air pollution, Agricultural activities -...

Agricultural activities - Cause of Air Pollution Agricultural activities too are a major cause of air pollution. About 60 to 65% of carbon dioxide is produced from burning of

What are diseases of the connective tissue, What are diseases of the connec...

What are diseases of the connective tissue? What are some of them? Diseases of the connective tissue are hereditary or acquired diseases(lots of autoimmune cause) characterized

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