Differentiation capacity of unincubated chick blastoderm in culture.

Unincubated (stage X) chick blastoderms cultured in plain Dulbecco's modified Eagle medium in the absence of serum, synthesize haemoglobin and melanin 2 . 5--3 . 0 and 6 . 0--7 . 0 days, respectively, after the beginning of culture. The capacity of unincubated blastoderm to form haemoglobin and melanin is a response to intrinsic genotypic instructions rather than to the active intervention of substances continuously supplied by the yolk. 5-Bromodeoxyridine, applied during the first and second days of unincubated blastoderm in culture, is incorporated into DNA and perturbs the formation of haemoglobin and melanin, perhaps, by modifying gene expression.