 She observed the effects of the transposition of Ac and Ds by the changing patterns of coloration in maize kernels over generations of controlled crosses , and described the relationship between the two loci through intricate microscopic analysis . She concluded that Ac controls the transposition of the Ds from chromosome 9 , and that the movement of Ds is accompanied by the breakage of the chromosome . When Ds moves , the aleurone @-@ color gene is released from the suppressing effect of the Ds and transformed into the active form , which initiates the pigment synthesis in cells . The transposition of Ds in different cells is random , it may move in some but not others , which causes color mosaicism . The size of the colored spot on the seed is determined by stage of the seed development during dissociation . McClintock also found that the transposition of Ds is determined by the number of Ac copies in the cell . 
