What causes chromosome breakage as opposed to insertion/excision without breakage?
Both Ds and Ac can move into and out of DNA, resulting in chromosome breakage or resealing of the DNA. Precise excision and resealing of the DNA happens most frequently (chromosome breakage is a mistake of the transposase), but this does not usually produce a visible phenotype. How can you tell whether variegation results from excision or breakage? See first questionall genes on one chromosome lost vs. only one gene. Also, an “unstable allele,” which results from excision of Ds/Ac to cause sectors, will look different from sectors arising from breakage. Basically, with breakage, the background of the kernel will look as expected from the genotype, with different sectors. With insertion/excision, the background of the kernel will be mutant (different from the genotype predicted from the cross), and the sectors will have the phenotype predicted from the cross (i.e. the background of normal, nonvariegated kernels). So with breakage, the kernel is normal/wt with mutant sectors, while with
