Most fish genomes are at least 1 billion nucleotide pairs long. However, the genome of the puffer fish Fugu rubripes is quite small at only about 0.4 billion nucleotide pairs, even though the number of Fugu genes is estimated to be comparable to that of its relatives which have larger genomes. What do you think mainly accounts for the Fugu genome being this small?

Question

Quizplus · Accepted Answer

The balance between the rates of DNA addition and DNA loss has been biased toward a net DNA loss in the Fugu lineage, resulting in a "cleansing" of functionally unnecessary sequences including most transposable elements and large parts of the introns. The exons, which are under purifying selection, were not affected as significantly.

Most Fish Genomes Are at Least 1 Billion Nucleotide Pairs