get a hybrid arrest at gastrula. Nucleoli then 

 start forming and the embryo lives for several 

 days but remains at the gastrula stage. This 

 system would appear to be well suited for this 

 type of study. We could not, however, obtain 

 any of the frogs. 



PAPACONSTANTINOU: Another question 

 relates to the volume in these embryos as 

 they approach gastrula. Is the total volume the 

 same? 



KOHNE: Well, it may not be but if there 



is a change it's so imperceptible that you don't 

 notice it. 



PAPACONSTANTINOU: If you looked at 

 this with an electron microscope, you wouldn't 

 be able to detect a decrease in the ribosomal 

 population per cell as it develops from the egg 

 to the gastrula? You're not synthesizing ribos- 

 omes, but your cells are dividing. I don't know 

 how many cells there are in a gastrula state 

 but I was wondering whether the total volume 

 of the whole embryo remains the same. 



(a) 4- DAY HAPLOID 



(b) 4-OAY CONTROL -|I500 



(e) 5- DAY CONTROL 



1500 



900 



300 



20 30 



TUBE NUMBER 



Fig. 5. 



Sedimentation patterns of RNA extracted from whole •'^P-labeledhaploid and control em- 

 bryos: a) 20 four-day-old haploid embryos, b) 20 four-day-old control embryos, c) 20 

 six-day-old haploid embryos, d) 20 six-day-old control embryos, e) 20 five-day-old con- 

 trol embryos. Sibling embryos were used in this experiment. 



43 



