Cheng, H.H., USDA, Agricultural Research Service, Avian Disease and Oncology Laboratory, East Lansing, Michigan 48823, USA.
Levin, I., USDA, Agricultural Research Service, Avian Disease and Oncology Laboratory, East Lansing, Michigan 48823, USA.
Vallejo, R.L., USDA, Agricultural Research Service, Avian Disease and Oncology Laboratory, East Lansing, Michigan 48823, USA.
Khatib, H., USDA, Agricultural Research Service, Avian Disease and Oncology Laboratory, East Lansing, Michigan 48823, USA.
Dodgson, J.B., USDA, Agricultural Research Service, Avian Disease and Oncology Laboratory, East Lansing, Michigan 48823, USA.
Crittenden, L.B., USDA, Agricultural Research Service, Avian Disease and Oncology Laboratory, East Lansing, Michigan 48823, USA.
Hillel, J., USDA, Agricultural Research Service, Avian Disease and Oncology Laboratory, East Lansing, Michigan 48823, USA.

Microsatellites are tandem duplications with a simple motif of one to six bases as the repeat unit. Microsatellites provide an excellent opportunity for developing genetic markers of high utility because the number of repeats is highly polymorphic, and the assay to score microsatellite polymorphisms is quick and reliable because the procedure is based on the polymerase chain reaction (PCR). We have identified 404 microsatellite-containing clones of which 219 were suitable as microsatellite markers. Primers for 151 of these microsatellites were developed and used to detect polymorphisms in DNA samples extracted from the parents of two reference populations and three resource populations. Sixty, 39, 46, 49, and 61% of the microsatellites exhibited length polymorphisms in the East Lansing reference population, the Compton reference population, resource population No. 1 (developed to identify resistance genes to Marek's disease), resource population No. 2 (developed to identify genes involved in abdominal fat), and resource population No. 3 (developed to identify genes involved in production traits), respectively. The 91 microsatellites that were polymorphic in the East Lansing reference population were genotyped and 86 genetic markers were eventually mapped. In addition, 11 new random amplified polymorphic DNA (RAPD) markers and 24 new markers based on the chicken CR1 element were mapped. The addition of these markers increases the total number of markers on the East Lansing genetic map to 273, of which 243 markers are resolved into 32 linkage groups. The map coverage within linkage groups is 1,402 cM with an average spacing of 6.7 cM between loci. The utility of the genetic map is greatly enhanced by adding 86 microsatellite markers. Based on our current map, approximately 2,550 cM of the chicken genome is within 20 cM of at least one microsatellite marker.