Answer:
25 nucleotide sequence pair
Explanation:
There are four nucleotide sequence pair present in DNA. and if we have 100 nucleotide so 25 nucleotide sequence pairs will be formed and each pair contains adenine (A), cytosine (C), guanine (G), and thymine (T).
Cytosine nucleotide paired with guanine nucleotide and Adenine nucleotide paired with thymine nucleotide . They have hydrogen bonds between each bases.  
 
        
             
        
        
        
Answer:
The meaningful differences between organisms in a population are genetic. Variations in the genome of members of a population arise through mutation. Occasionally, a mutation occurs in an individual that is beneficial, that helps that organism be better able to survive and repoduce in its current environment.
 
        
             
        
        
        
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Nitrogen fixation is the process by which nitrogen gas from the atmosphere is converted into different compounds that can be used by plants and animals. There are three major ways in which this happens: first, by lightning; second, by industrial methods; finally, by bacteria living in the soil.