Maize (Zea mays L.) breeders commonly classify inbred lines into heter
otic groups based on pedigree information and/or combining ability. Th
ese heterotic groups influence how germplasm is used, and have increas
ed the efficiency of breeding programs. The most widely recognized and
exploited heterotic pattern in the U.S. Corn Belt is that of Reid Yel
low Dent by Lancaster Surecrop. Pedigree information was used to exami
ne the diversity present in 37 publicly developed inbreds of the Lanca
ster Surecrop heterotic group, and to investigate the evolution to its
present state. All of the Lancaster Surecrop germ-plasm in the public
ly developed inbreds included in the modern Lancaster Surecrop heterot
ic group was derived from two inbreds, Oh40B and C103. Furthermore, th
e amount of true Lancaster Surecrop germplasm is 50% or less in 36 of
these inbreds, with >20 non-Lancaster Surecrop sources contributing ge
rmplasm to this heterotic group. The Lancaster Surecrop heterotic grou
p has been modified considerably, with a reduction in Lancaster Surecr
op germplasm and an increase in non-Lancaster Surecrop germplasm inclu
ding Reid Yellow Dent.