Chicken microchromosomes are hypermethylated and can be identified by specific painting probes.

Microdissection of single chicken microchromosomes (MICs) followed by degenerate oligonucleotide-primed (DOP) PCR allows the rapid generation of MIC-specific DNA libraries. Since some libraries derived from a single (or a few) chromosome(s) label the entire MIC fraction, the majority of chicken MICs share repetitive DNA sequences that are not found on the macrochromosomes. In evolutionarily distant bird species, MICs are invariably hypermethylated. Methylcytosine staining provides additional in situ evidence for the high gene content of MICs and strong compartmentalization of avian genomes.