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!
Many definitions of species have been offered, but none of them proved to be satisfactory. The definitions did not categorically provide the basis to decide whether two similar groups are distinct species or only sub-species. Again what is the criterion to decide the distinctness of a species? Some tried to specify the degree of difference that would distinguish a species from another. Apart from the difficulty in quantifying such differences, there are also other problems. Certain forms which show very little morphological differences proved to be very distinct species. In other cases, such as Homo sapiens, undoubtedly a single species, different races have pronounced differences. The discontinuity between groups, it appears, depends less on the degree of differences and more on the constancy of differences. Another approach to define species was to distinguish related organisms on their inability to breed. Many definitions of species have relied upon such interspecific sterility and sterility of offsprings, that is hybrid sterility. This proposition also has certain inherent problems. It is not easy to identify cases in which organisms do not interbreed, and those which can breed, but do not do so for certain reasons. At these times, sterility cannot be deemed to be an appiopriatc criterion for defining species. Nevertheless, reproductive isolation or inability to breed has been the commdn element in the definition of species provided by many evolutionary biologists, be it Dobzhansky, Goldschmidt or Ernst Mayr. Reproductive isolation, the discussion of which follows later in this unit, has been the basis for defining the species and speciation.' Such an isolating mechanism becomes a barrier for the flow of genes between related populations and the concept of biological species centres around this phenomenon.
Normal 0 false false false EN-IN X-NONE X-NONE MicrosoftInternetExplorer4
Phase Contrast Microscopy Phase contrast microscope has the resolving power similar to ordinary light microscope. However, it enables us to observe the cellular organelles in liv
Gastro Epiploic Artery (GE) : Gastro epiploic artery is a less popular arterial conduit now. The midline chest incision is extended to the umbilicus and the right ga
Food-borne Clostridium Clostridium botulinum and Cl. perfringens, the two members of the group have been implicated in food-borne illnesses. C. botulinum causes classical food
Intramuscular Route of Injection Purpose When rapid action is required. When drug would prove irritating to the subcutaneous tissue. Site selected must be whe
What is a biodigester? A biodigester is equipment that creates carbon dioxide, hydrogen sulfide and fuel gases (biogases) like methane from organic material under decomposition
Explain Synergistic Contribution of Malnutrition to Child Mortality? The synergistic contribution of malnutrition to child mortality is consistent across populations and can be
Q.Define Cardiac catheterization and angiography? The purpose of this unit is to give you an overview and insight into the world of Cardiac Catheterization and Angiography. Thi
SEXUA L REPRODUCTION 1 . Amphigony - Zygote is formed. (i) Syngamy Fusion of gametes. (a) Endogamy - It involves self fertilisation. e.g.
IAA Stimulates Cell Enlargement Cell wall contains layer of cellulose fibrils and are normally quite rigid. Thus for a cell to grow, there must be a mechanism for relaxing th
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: +1-415-670-9521
Phone: +1-415-670-9521
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd