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.
(a) Give two examples of diseases which can be spread by contaminated drinking water. (b) How can the spread of such diseases be prevented? (a) Typhoid and cho
Explain about the Zygomycota - Fungi? Fungi belonging to zygomycota are called zygomycetes. Hyphae in this sub-class are coenocytic. Asexual spores develop in sporangia at the
Dyslipidemia is an important correctable factor for Coronary Artery Disease. There is a strong, independent, continuous, and graded relation between total cholesterol (TC) or low-
Subtropical rain forests - Ecosystem In regions of fairly high rainfall but less temperature differences between winter and summer and broad-leaved evergreen subtropical biome
Role of Pancreas in Digestion Pancreatic juices secreted from the pancreas aid in digestion of the food. About 600-800 ml of fluid i.e. the pancreatic juice is
Brain Brain is a part of central nervous system which lies in the skull. Source: Sears and Windwood, Anatomy and Physiology for Nurses The different parts of the bra
What is Schistosomiasis? Explain in brief. A disease cause by the trematode parasite Schistosoma found around the world. Numerous species are responsible for diseases ranging f
Define Methods of Estimation of Energy Expenditure and Requirements? There are a variety of methods available to measure human energy expenditure. Knowledge of these methods wi
Oil seed meals as source of limiting amino acids Generally ruminants are not perceived to have a requirement for essential amino acids as the rumen microbes can synthesis esse
Is the effect of genetic drift likely to be the same in pop 1 and pop 2? How are genetic drift and pop size related? when there is strong selection against the homozygous recessive
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