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in the absence of any large scale envirorrmental change that is in more or less uniform environments populations often maintain a stable genetic
while discussing the darwinian premise of natural selection we observed that the term selection is synonymous with non-random reproduction and that
sickle cell anaemia in man is caused by a defective chain of haemoglobin the abnormal haemoglobin known as mbs differs from natural haemoglobin hha
in the previous sub-section we discussed the possible ways by which variabiliti can be generated we shall now examine one instance that illustrates
mutations are the only kind of variability generating mechanism in prokaryotes and asexually reproducing organisms but in eukaryotes where sexual
each gene has a characteristic mutation rate mutation rates are often described as an average per gene basis for instance drosophila has one
the original dna sequence when transcribed and translated would yield five successive valine residues but the altered sequence would correspondingly
gene or point mutations occur when the dna sequence of a gene is altered and the new nucleotide sequence is passed on to the offspring this occurs
aneuploidy one or inore chronosomes of a normal set nlay bc lacking or present in excess the term riullisony refers to absence of both the
mutations and genetic recombination in sexually reproducing organisms are major sources of variations in natural populations in this section we will
in the preceding section we emphasised the fact that cvolution or the continuous adaptations to the environment can take place only when pheiiotypes
natural selection can therefore mean differential reproduction among members of the sarne gene pool we earlier said that selection would promote
assuming that variability of populations were non-genetic that is not controlled by genetic material once again chance events alone would determine
variability refers to the differences in heritable traits exhibited by the individuals of a species one of the major contributions of darwin to the
organisms are made to compete for their needs from the environment the competition as we pointed earlier could be for the food and territory to
by prodigality of nature it is meant that organisms have an enormous potential to reproduce a carp or salmon is known to lay over a million eggs a
darwin put fort the notion of the survival of the fittest how do we define fittest the answer usually given is those who survive so you can readily
in that unit you also learnt about darwin who based on his extensive observations and interpretations showed that evolution is a simple fact of
the effect of natural selection on colonies or population favouring one group in preference to other may be referred to as group selection a group
before we proceed to discuss kin selection we should define the term altruism it refers to the behaviour pattern of an individual in the population
while explaining the concept of natural selection we have stressed the fact that natural selection is synonymous with differential or non-random
in this section you will be introduced to a variant of darwinian concept of natural selection which he termed sexual selection you may have observed
tonicity and the plant cell table 3 amount of water displaced by potato samples before and after
coevolutionary relationships between parasites and their hosts can be more complicated than between predators and their prey as in the case of
there has been a perfect coevolution between plants and herbivorous animals this has often developed into a mutually beneficial relationship whereas