Mapping of the chicken N‐CAM gene and a myosin heavy chain gene: Avian microchromosomes are not genetically inert reserves of DNA

Physical mapping of the chicken neural cell adhesion molecule gene and of a chicken myosin fast-white heavy chain gene via in situ hybridization has assigned both loci to different-sized microchromosomes in this species. Two genomic cloned chicken DNA probes of 16 kb (lambda cN6) and 15 kb (DCM 11), respectively, were biotin labeled for fluorescent detection of the genes. The implications derived from these results, together with further data just now beginning to accumulate regarding the genetic content of avian microchromosomes, confirm an unexpectedly active role for these minute chromosomes.