AUTORADIOGRAPHIC STUDIES 



OF H'-THYMIDINE INCORPORATION 



IN NORMAL AND HYBRID FROG EMBRYOS 



BETTY C. MOORE 



Department of Zoology, Columbia University, New York 



Incorporation of tritiated thymidine by the early embryos of diploid and 

 androgenetic haploid R. pipiens and diploid and androgenetic haploid 

 hybrids between R. pipiens^ y- R. sylvaticaO has been studied. Two 

 sorts of experiments were carried out. In one, H^-thymidine was injected 

 into an adult female pipiens and the radioactive eggs utilized. In the 

 other, H^-thymidine was injected directly into the eggs before first 

 cleavage. 



It has been demonstrated that there is an increased utilization of 

 H'-thymidine at the blastula stage as compared to early cleavage stages. 

 It is concluded that cytoplasmic deoxyribopolynucleotides are used in 

 chromosomal replication at early cleavage stages. 



In (pip) syl embryos, utilization of pipiens cytoplasmic deoxyribo- 

 polynucleotides by sylvatica chromosomes in their replication could 

 resuit in inexact copies of the genetic material, which would lead to 

 abnormal development. 



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