Figure 1.

The abnormal chromosome 10 (Ab10) haplotype in Z. mays. (A) Chromosome models of different haplotypes of chromosome 10 in Z. mays. The locations of centromeres (yellow), TR-1 (red), and Knob-180 (green) repeats are colored as shown. The locations of marker loci Colored1 (R1), White seedling2 (W2), Opaque endosperm7 (O7), Luteus13 (L13), and Striate leaves2 (Sr2) are listed below their relative positions. Note that in the Ab10-I, Ab10-II, and Ab10-III haplotypes, the relative ordering of W2, O7, and L13 is inverted in what is known as the shared region. K10L2 contains these same genes but their order and position relative to its knob is unknown. N10 indicates normal chromosome 10. (B) The Rhoades model of neocentromere-mediated meiotic drive. Knobs are shown in red (representing both the 180-bp knob repeats and TR-1 repeats), centromeres are in blue, and spindle fibers are in green. Meiotic drive requires that recombination occurs between the centromere and the Ab10 haplotype (and between centromeres and knobs on other chromosomes). Neocentromere activity, encoded by genes on Ab10, causes Ab10 and other knobs to move along microtubules, creating a polar arrangement that persists through metaphase I, anaphase I, metaphase II (data not shown), and anaphase II. The result is that Ab10 and other knobs end up in the upper and lower cells of the linear tetrad. As only the bottom-most cell will become a viable gamete, Ab10 and other knobs are preferentially transmitted. (C) Map of where the Ab10 haplotypes used in this study were originally collected.