The genomic content of the nucleus is constant for a given species whereas the extrachromosomal DNA is found to be variable among the members of a population. Explain.
Ans. The genomic content of the nucleus is constant for a given species which imparts specific characters to the species. Each species has its own unique set of characters which is entirely different from any other species. DNA is the carrier of traits and genetic information from one generation to another. The chromosomes that carry the DNA are fixed for particular organisms. A human cell contains 23 pairs of chromosomes. Had this unique set of chromosomes not existed, humans would not have got their special characteristics which make them human or cats would not look like cats or dogs would not give birth to puppies.
In case of extra genomic DNA, the number can vary because these are not responsible for the transfer of genetic traits from one generation to another, but these are only responsible for replication of a cell organelle in which they are present like the DNA present in the mitochondria and plastids.
Therefore, the genomic content of the nucleus is always constant for a given species, but the extra genomic content can vary among the members of the same species.