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Organisms look similar because their body designs are similar. If body designs are to be similar, the blue prints for these designs should be similar. Thus, reproduction involves making copies of the blueprints of body design. The chromosomes in the nucleus of a cell contain information for inheritance of features from parents to next generation in the form of DNA(Deoxyribo Nucleic Acid) molecules. The DNA in the cell nucleus is the information source for making proteins. If the information is changed, different proteins will be made. Different proteins will eventually lead to altered body designs. A basic even in reproduction is the creation of a DNA copy. Cells use chemical reactions to build copies of their DNA. The process of copying DNA will have some variations each time. The DNA copies generated will be similar but may not be identical to the original
The consistency of DNA copying during reproduction is important, which leads to the stability of population species.
Changes in ecological system, which are beyond our control like varying temperature, varying water levels and natural calamities, can wipe out the population species.
So if there is some variations are present in some individuals of the population species then there is a chance for the survival of these species over time
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