  Maize Abnormal chromosome 10 (Ab10) contains a classic meiotic drive system
that exploits asymmetry of meiosis to preferentially transmit itself and other
chromosomes containing specialized heterochromatic regions called knobs. The
structure and diversity of the Ab10 meiotic drive haplotype is poorly
understood. We developed a BAC library from an Ab10 line and used the data to
develop sequence-based markers, focusing on the proximal portion of the
haplotype that shows partial homology to normal chromosome 10. These molecular
and additional cytological data demonstrate that two previously identified Ab10
variants (Ab10-I and Ab10-II) share a common origin. Dominant PCR markers were
used with FISH to assay 160 diverse teosinte and maize landrace populations
from across the Americas, resulting in the identification of a previously
unknown but prevalent form of Ab10 (Ab10-III). We find that Ab10 occurs in at
least 75% of teosinte populations at a mean frequency of 15%. Ab10 was also
found in 13% of the maize landraces, but does not appear to be fixed in any
wild or cultivated population. Quantitative analyses suggest that the abundance
and distribution of Ab10 is governed by a complex combination of intrinsic
fitness effects as well as extrinsic environmental variability.
