Incorporation of Tritium-labelled Thymidine in Bufo ♀ × Rana temporaria ♂ Hybrid Embryos

Abstract

IT is well known that cross-fertilization can often be performed in amphibians; development, in anurans, often does not proceed further than the late blastula or early gastrula stage. The reasons why this block in development occurs are not yet well known. I hoped that an autoradiographic study of the incorporation of nucleic acid and protein precursors into lethal hybrids might help in elucidating the problem. The precursor used in this work is tritium-labelled thymidine. B. C. Moore¹ has shown that this precursor, if injected into female Rana pipiens before ovulation, is incorporated, at the morula stage, in the nuclei of normal Rana pipiens and of androgenetic pipiens embryos. Thymidine is also incorporated into the deoxyribonucleic acid of the lethal diploid hybrids pipiens ♀ × sylvatica ♂.