The genome sequence of the sei whale, Balaenoptera borealis (Lesson, 1828) (Artiodactyla: Balaenopteridae)

<ns3:p> We present a genome assembly from an individual female <ns3:italic>Balaenoptera borealis</ns3:italic> (sei whale; Chordata; Mammalia; Artiodactyla; Balaenopteridae). The assembly contains two haplotypes with total lengths of 3 234.56 megabases and 2 988.82 megabases. Most of haplotype 1 (79.31%) is scaffolded into 22 chromosomal pseudomolecules, including the X sex chromosome. Haplotype 2 was assembled to scaffold level. The mitochondrial genome has also been assembled, with a length of 16.41 kilobases. Gene annotation of this assembly on Ensembl identified 18 485 protein-coding genes. This assembly was generated as part of the Darwin Tree of Life project, which produces reference genomes for eukaryotic species found in Britain and Ireland. </ns3:p>