The DNA content of the nucleus is constant for a given species. The haploid organisms have half the content of DNA than that of their diploid parents. The amount of DNA remains constant in all the members of a given species. On the other hand, the extrachomosomal DNA which occur either in the mitochondria or in chloroplast is found to be variable among the members of a population. In case of highly active organisms, the DNA (extrachromosomal) is found to be more as compared to less active ones.