To identify CR events, we performed a systematic marker
order comparison between the chromosomes of donkey, zebra,
and horse using an appropriate panel of horse BAC clones for
each chromosome. The primary constriction was used as a
marker for centromere localization. The clones specific for
chromosomes for which detailed and informative results were
obtained are reported in Table 1. Precise marker order definition
for the remaining chromosomes was precluded by (i) the
complex rearrangements that differentiated some donkey
chromosomes from their zebra and/or horse homologs, (ii) the
very small size of some chromosomes, and (iii) the occasional
lack of appropriate probes. Seventy-seven informative BAC
clones were selected by screening the CHORI-241 horse BAC
library using locus-specific ‘‘overgo’’ probes designed on the