Insertion and removal (Ds)

As defined by McClintock, an activator (Ac
locus) is an element that can activate another
locus, dissociation (Ds), and cause a break in the
chromosome (1). While Ac can move independently
(autonomous transposition), Ds can only
move to another location of the chromosome
under the influence of Ac (nonautonomous
transposition). The C locus is inactivated by the
insertion of Ds (2). Under the influence of Ac, Ds
is then removed from some of the cells, and the
C locus is returned to normal function. Since the
cells of corn are of clonal origin, the time of
transposition influences the phenotype. If
transposition occurs early in development, the
pigmented spots are relatively large; if it occurs
late, the spots are small.