A physical map of the 1-gigabase bread wheat chromosome 3B

As the staple food for 35% of the world's population, wheat is one of the most important crop species. To date, sequence- based tools to accelerate wheat improvement are lacking. As part of the international effort to sequence the 17- billion- base- pair hexaploid bread wheat genome ( 2n = 6x = 42 chromosomes), we constructed a bacterial artificial chromosome ( BAC)based integrated physical map of the largest chromosome, 3B, that alone is 995 megabases. A chromosome- specific BAC library was used to assemble 82% of the chromosome into 1036 contigs that were anchored with 1443 molecular markers, providing a major resource for genetic and genomic studies. This physical map establishes a template for the remaining wheat chromosomes and demonstrates the feasibility of constructing physical maps in large, complex, polyploid genomes with a chromosome- based approach.