Constructing defined chromosome segmental duplications in maize

We describe the production of chromosome segmental duplications and deletions of defined length in maize. The method utilizes a collection of previously isolated transposon-induced reciprocal translocations with sequence-defined breakpoints. These balanced translocations involve a first common breakpoint at the site of transposon Ac/fAc insertions on chromosome 1S, and a second variable endpoint elsewhere in the genome. Stocks containing translocations with different endpoints on the same chromosome arms were crossed together to generate heterozygous combinations. Subsequent meiotic segregation generates gametes that contain the original balanced translocations, or pairs of translocation chromosomes that are genetically unbalanced; i.e., they contain a duplication or deletion of the affected segment. Self-pollination produces progeny plants that are genetically balanced, or that contain 0 to 4 copies of the affected segment. The chromosome constitution of progeny plants can be determined using PCR primers flanking the translocation breakpoints. In addition, plants segregating genetically unbalanced gametes exhibit significant pollen grain abnormalities and thus can be easily detected in the field. In this way, we constructed 4 different segmental tetrasomic stocks involving genomic regions of approximately 7.8, 18.7, 21, and 42.6 Mb on chromosomes 5S, 5L, 5L, and 4L, respectively. FISH analysis using specific probes located within the affected segments confirms their aneuploid composition. These and similar lines containing precisely defined segmental duplications and deletions may be useful to study the genetic impact of gene dosage.