Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
In this section, we shall discuss a classic example of natulal selection in action. In the preceding unit, it was stated that natural selection always aims at eliminating alleles, which are less adapted to the environment. Conversely selection indirectly aims to promote those alleles or individuals that are well adapted to a given environment.
The promotion and establishment of an allele and the resultant phenotype may take several hundreds of years in natural populations. But there are indeed instances where the selective forces have brought changes in the character of individuals within historical times.
The peppered moths Biston betillaria occur in two forms, the melanic and non-melanic. As shown in Fig. the melanic forms are black in colour and non-mel?nic ones are mottled grey. Until the early part of the 19th century, the melanic forms were regarded as rare and prize collections by insect collectors, and the light non-melanic forms were abundantly present in natural populations. The rarit.? of black forrns was essentially due to the higher rate of predation by birds. The black forms resting on light coloured and lichen encrusted trees were the easy targets for the birds. The light coloured non-melanics blend with their background, and therefore, are not easily visible to the predators. With the onset of the industrial revolution the distribution of melanic forms particularly in the industrial centres underwent a great change. An examination of museum collection of insects over the past 100 years showed that the melanic forms increased in numbers and the non-melanics were becoming rarer and rarer. What could be the possible reason for such an occurrence? In industrial regions, the sooty smoke emanating from factories blackened the bark of the trees and prevented the growth of lichens. This resulted in the black coloured forms resting on such trees becoming invisible to the p~edators and the light coloured ones being increasingly susceptible to the predator attack because of their contrast with the background. In industrial areas the birds predated upon non-melanics in extremely large numbers whereas in other areas melanics were preferentially caten. Since the proportion of melanics increased due to industrial activity, the examplc is often referred to as industrial melanism.
Proteins of Plant Origin - Cereal Proteins Cereal Proteins: Cereal grains, properly ripened and dried for optimum storage stability, have protein content ranging from 6-20%.
How do the plants classify according to their photoperiodism-based flowering? According to their photoperiodism-based the flowering plants classify as long-day plants, those th
CONDITIONE D REFLEX - Response which is achieved by training is conditioned reflex. I. P. Pavlov in 1920 displayed it by experimenting on dog. These are voluntary in
What is the defense mechanism that begins to work when inflammation fails to stop an infection? If the inflammatory attack is not enough to halt the infectious process the body
Serogroups Five major serogroups of N. meningitidis, A, B, C, Y and W-135, cause most human infection. Serogroup A is the leading cause of disease in the "meningitis belt" acr
Male reproductive system of frog: i) Testis : a) There are a pair of testis which are attached to the kidneys. b) They are oval and yellow in colour. c) Inside the testis th
Define General procedure of titration - Nutritional Biochemistry? In general a titration requires that we add precise amounts of the known titrant to the unknown analyte or ti
An insect collecting net A useful insect net can be made from a round stick such as a broom or mop handle, some heavy wire and mosquito netting or cheese cloth. Bend a heavy pi
Development Projects - Deforestation The use of science and technology to support the ever- increasing needs of man is termed as development. In the recent years, the human po
Q Why do protease-supplying cells of the stomach and of the pancreas make only precursors of the active proteolytic enzymes? The stomach and the pancreas make zymogens of the p
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!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd