Most Fish Genomes Are at Least 1 Billion Nucleotide Pairs

Multiple Choice

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?

A) Evolutionary advantage of extremely small exon sizes in the Fugu lineage
B) Unusual disappearance of all intronic sequences from the Fugu genome
C) Increased abundance of transposable elements in the Fugu genome
D) Increased occurrence of mitotic whole-chromosome loss in the Fugu lineage
E) Low relative rate of DNA addition compared to DNA loss in the Fugu lineage