Deoxynucleic acid in some gametes and embryos 



DNA IN GAMETES AND EMBRYOS OF PARAC EN TROTU S LIVIDUS 



Material. The work was carried out at the Stazione Zoologica, Naples. To 600 ml. of 

 an egg suspension containing about 4 x io 4 eggs per ml. in sea water there was 

 added 0-5 ml. of a sperm suspension containing about 10 sperms per egg. The egg 

 suspension was placed at 20 G. and continuously mixed by a slow stirrer. 



To fix the fertilized eggs or embryos for microscopic examination 9 ml. of the 

 suspension were withdrawn and added to one ml. of 40 per cent, formalin. For the 

 DNA determination 40 ml. of the suspension were withdrawn, cooled in ice water 

 and centrifuged at low speed. The embryos were suspended in 40 ml. of acid sea 

 water at pH 36 to remove the jelly capsule and adhering sperms, and again centri- 

 fuged. The washing with acid sea water was repeated once and followed by one 

 washing with 40 ml. of distilled water to remove salts. The embryos were washed 

 twice with acetone and once with ether and then dried in a vacuum desiccator over 

 sulphuric acid. Washing and centrifuging were performed at o° G. with precooled 

 fluids. The treatment described above is without effect on the DNA content of the 

 eggs. 



Results 



(1) DNA in sperm and unfertilized eggs: 



(a) sperm 



20 ml. sperm suspension ^ 60 mg. dry matter 

 1 /xl ,, ,, ~o-5i X 1 o 6 sperm 



1 mg. dry matter ~ 390 m/xmol. deoxyriboside 



390 x 60 x o 310 „ __ . 



per sperm: — — - — ^ =071 x io- 6 ug- DNA 



051 x io 6 x 20 x io 3 ^ & 



(b) eggs 



40 ml. egg suspension ^ 70 mg. dry matter 

 1 ml. „ „ ~4-4 X io 4 eggs 



1 mg. dry matter ■ — ' 1 35 mju,mol. deoxyriboside 



1 3S X 70 x 0310 „ „ 



per egg: — ^ J— 6 — = 166 x io" 6 ug. DNA 



4-4 x io 4 x 40 r& 



DNA per egg 166 



DNA per sperm 071 



23 



Elson and Chargaff (1952), using a microbiological assay of thymine, found about 

 25 X io- 6 jitg. DNA per egg and 1 o x io~ 6 ^g. DNA per sperm. 



83 



