Deoxynucleic acid in some gametes and embryos 



average per egg: 7 3 X io -2 fig. DNA 



DNA per egg 73 x 10 



-2 



•5 X io J 



DNA per sperm 8-6 x io~ 6 



The value found for the DNA content per sperm seems high, but it agrees well with 

 the finding by Mirsky and Ris (1949), that erythrocytes of the frog contain 150 X 

 io~ 6 /xg. DNA per cell and hepatic tissue 157 X io -6 fig. DNA per cell. If we take 

 the average value 15 35 x io~ 6 fig. as representing the DNA content of the diploid 

 cells of the frog we get : 



DNA per egsr 73 x io -2 



^ ATA F ^ = - L ^ r = 475 X io 3 



DNA per cell 1535 x io- 6 * /J 



which means that the egg contains enough DNA for about 5000 cells. 



(2) DNA in embryos during the early stages of development (i3°-i7° C.) : 



h 8/2/6 20 2h 28 



hours after ferii/izafion. temp. /f-/7°C. 



Figure 3. Content of DNA in eggs and embryos of Rana temporaria. 

 The figures above the curve indicate Shumwafs stages of development. 



Figure 3 shows that the content of DNA in the embryo is the same as in the unfertil- 

 ized egg until 18 hours after fertilization (Shumway's stage 9). At that stage a rapid 

 synthesis of DNA begins. 5,000 cells at that time would correspond to an average 

 generation time of about i\ hours. 



DNA IN EGGS AND EMBRYOS OF THE DOMESTIC FOWL 



Material. Fertilized eggs were incubated at 38 C. and 70 per cent, humidity. 

 2x2 eggs were taken out daily at the same time of day and treated as follows : 

 2 whole eggs (white, yolk and embryo) were treated in a blender with 500 ml. of 



85 



