The Brown Norway (BN) rat genome sequence, the third complete mammalian genome, provides insights into mammalian evolution. The BN rat genome is 2.75 gigabases, smaller than the human genome but larger than the mouse genome. The sequence is a high-quality draft, covering over 90% of the genome. Comparative analysis with the human and mouse genomes reveals details of mammalian evolution, including gene and protein relationships, repeated sequences, chromosomal rearrangements, and lineage-specific events. The rat genome has a higher rate of segmental duplications and microdeletions compared to the mouse genome, suggesting more active evolutionary processes in the rodent lineage. The study also highlights the importance of the rat as a model organism in biomedical research, contributing to advancements in drug development and disease understanding.The Brown Norway (BN) rat genome sequence, the third complete mammalian genome, provides insights into mammalian evolution. The BN rat genome is 2.75 gigabases, smaller than the human genome but larger than the mouse genome. The sequence is a high-quality draft, covering over 90% of the genome. Comparative analysis with the human and mouse genomes reveals details of mammalian evolution, including gene and protein relationships, repeated sequences, chromosomal rearrangements, and lineage-specific events. The rat genome has a higher rate of segmental duplications and microdeletions compared to the mouse genome, suggesting more active evolutionary processes in the rodent lineage. The study also highlights the importance of the rat as a model organism in biomedical research, contributing to advancements in drug development and disease understanding.