Fat, juicy tomatoes may be the norm in modern supermarkets; wild tomatoes can be 1,000 times smaller. Biologists at Cornell University in Ithaca, New York, have identified a major genetic determinant of large tomato size that increases the number of female reproductive organs in a tomato flower, and thus the number of compartments in the fruit.
The determinant, 6-8-kilobases long, is in a gene called fas, named by Steven Tanksley and his colleagues. The team crossed tomatoes of varying girth and mapped the genetic region that conferred the tomatoes' compartment number. The insertion in fas is probably a mutation that occurred during tomato domestication; it was not present in 30 lines of the wild tomato from which domestic tomatoes are thought to descend.