IDENTIFICATION OF 16 CHICKEN MICROCHROMOSOMES BY MOLECULAR MARKERS USING 2-COLOR FLUORESCENCE IN-SITU HYBRIDIZATION (FISH)

A feature of avian karyotypes is the presence of microchromosomes. As a typical avian genome, the chicken karyotype (2n = 78) consists of ni ne pairs of macrochromosomes, including the W and Z sexual chromosomes , and 30 pairs of indistinguishable microchromosomes usually ordered a rbitrarily by decreasing size. Despite their reduced size, microchromo somes represent one-third of the genome and have a high gene density. So as to provide a tool to identify them, we developed a set of large insert-containing clones to be used as tags in two-colour fluorescence in situ hybridization experiments. Seventeen clones, six of which con tain a microsatellite sequence and two others the fatty acid synthase gene or genes from the major histocompatibility complex, all presentin g a strong hybridization signal, were selected for this purpose and en abled us to identify 16 different microchromosomes. The ability to rec ognize individual microchromosomes will be of great value for cytogene tic gene mapping, assignation of linkage groups from genetic maps and other studies on avian genome structure.