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heredity and evolution

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
Give an example of characteristics being used to determine how close two species are in evolutionary terms.

Structure of forelimb in a frog, lizard, bird and horse is similar with similar bones which are modified to suit the function they perform. From this it can be safely assumed that they may have evolved from a common ancestor.


What factors could lead to the rise of a new species?

Factors that could lead to the rise of a new species are:
i. Accumulated variations favourable to the changing natural environment.
ii. Geographical isolation of a population.
iii. Natural selection.
iv. Action of different environmental factors on these isolated populations.
v. Reproductive isolation and change of number of chromosomes.

Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

The smaller number of tigers means lesser variations which in turn means lesser ability to adapt to the changing environment. For example, if a deadly disease infects the tigers, all the tigers may die from it as there would be less variation in the genotype to survive the disease. Decrease in population of tigers also indicates that tiger variants are not adapted to the existing environment and may become extinct soon.

Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?

No, Asexually reproducing organisms have very little variation over generations as they involve only one parent. The variations result from the DNA mutations . But these variations are very few and are not capable of giving rise to a new species. Thus geographical isolation will not be a major factor in the speciation of the orgnaism that reproduces asexually.

Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?

No, as the population is self pollinating it would be less prone to factors which result from geographical isolation. Since the same plant is involved in the pollination there will be no variations and thus no speciation will be there.