Autoradiographic studies of rabbit ova after fertilization with thymidine-H3 and -C14 labelled spermatozoa originating from different bucks.

Rabbit spermatozoa were labelled in vivo injecting male rabbits with thymidine-H3 and thymidine-C14. Ova fertilized with H3-labelled spermatozoa were found to contain more silver grains when they had cleaved several times than before cleavage. Fertilized ova originating from rabbits that had been mated with both an H3- and C14-thymidine labelled buck carried both labels. An explanation for this phenomenon may be that additional spermatozoa in the perivitelline space of fertilized ova pass labelled DNA-bases to the cleaving blastomeres.