In a manner that is specific to the genotypes involved in the cross, the copy number of a repeated sequence can be dramatically different from Mendelian expectation. Progeny from 25 crosses including reciprocals have been analyzed. A sample of the data is given below. The change is not random. A particular genomic change is found each time a cross is made and in all progeny of that cross.
Reciprocal crosses result in the same genomic changes.
Neither the occurrence of F1 change nor the magnitude of the change is related to the copy numbers or difference in copy numbers of the parental lines. The direction of copy number change is consistent for each sequence. In the data we have collected so far, rDNA and SS sequences either show the parental mean or a decrease in number, whereas a sequence associated with chromosome knobs, pZmK10, and one that might have a role in DNA replication pZmA101, have only shown changes that are increases over expected values. Experiments are in progress to explore the timing, genetics and developmental ramifications of this rapid genomic change. Measurements are being made on DNA samples from early embryonic tissue of both F1 and inbred plants to determine when genomic changes take place.