YAC Library Storage and Transport

The development of the yeast artificial chromosome (YAC) cloning system (1 ) and the construction of YAC libraries with large numbers of genome equivalents (2 –6 ) provided a major impetus to mammalian genome mapping. These technical advances enabled the mapping of megabase-sized chromosomal regions (7 ,8 ), culminating in the first complete clone maps of single mammalian chromosomes (9 ,10 ).